Awesome .NET!

A collection of awesome .NET libraries, tools, frameworks, and software.

Inspired by awesome-ruby, awesome-php, awesome-python, frontend-dev-bookmarks and ruby-bookmarks.

Contributions are always welcome! Please take a look at the contribution guidelines and quality standard pages first. We accept proprietary and commercial software too.

Thanks to all contributors, you're awesome and wouldn't be possible without you! The goal is to build a categorized community-driven collection of very well-known resources.

License

To the extent possible under law, Vitali Fokin has waived all copyright and related or neighboring rights to this work.

Algorithms and Data structures

Algorithmia - Algorithm and data-structure library for .NET 3.5 and up. Algorithmia contains sophisticated algorithms and data-structures like graphs, priority queues, command, undo-redo and more.
C# Algorithms - A C# plug-and-play class-library project of standard Data Structures and Algorithms. It contains 35+ Data Structures and 30+ Algorithms designed as Object-Oriented isolated components.
Towel - data structures, algorithms, mathematics, metadata, extensions, console, measurements, and other useful stuff
Akade.IndexedSet - A convenient data structure supporting efficient in-memory indexing and querying, including range queries and fuzzy string matching.

API

Telegram.Bot - .NET Client for Telegram Bot API
TLSharp - It's a perfect fit for any developer who would like to send data directly to Telegram users or write own custom Telegram client.
WTelegramClient - Automate a user account on Telegram, using the latest version of Telegram Client API
NancyFx - Lightweight, low-ceremony, framework for building HTTP-based services on .NET and Mono
ASP.NET Web API - Framework that makes it easy to build HTTP services that reach a broad range of clients, including browsers and mobile devices
Breeze - API framework enabling rich data access by using the OData 3 protocol. Client libraries available for JavaScript and C#.
Mobius: C# API for Spark - Mobius adds C# language binding to Apache Spark, enabling the implementation of Spark driver code and data processing operations in C#.
ServiceStack - Thoughtfully architected, obscenely fast, thoroughly enjoyable web services for all
Nelibur - Nelibur is message based web service framework on the pure WCF. Nelibur simplifies creating high-performance and message-based web services and you certainly have all the power of the WCF.
WebAPI Contrib - Collection of open source projects to help improve your work with ASP.NET Web API
Xamarin.Essentials - Xamarin.Essentials provides developers with cross-platform APIs for their mobile applications.
FFImageLoading - Fast & Furious Image Loading - This Library to load images quickly & easily on Xamarin.iOS, Xamarin.Android, Xamarin.Forms, Xamarin.Mac / Xamarin.Tizen and Windows (UWP, WinRT)
Ocelot - .NET core API Gateway
CommandQuery - Command Query Separation for 🌐ASP.NET Core ⚡AWS Lambda ⚡Azure Functions ⚡Google Cloud Functions 🌐ASP.NET Web API 2
Cloud Storage:- This library provides a universal interface for accessing and manipulating data in different cloud blob storage providers (Azure Storage, AWS S3, Google Cloud Storage. It makes it easy to switch between providers or to use multiple providers simultaneously, without having to learn and use multiple APIs.

Application Frameworks

.NET Boxed Framework - .NET Core Extensions and Helper NuGet packages
ASP.NET Boilerplate - A starting point for new modern ASP.NET MVC web applications with best practices and most popular tools.
ABP - The next generation of the ASP.NET Boilerplate web application framework.
Orleans - Orleans is a framework that provides a straight-forward approach to building distributed high-scale computing applications, without the need to learn and apply complex concurrency or other scaling patterns
Newbe.Claptrap - This is a set of server-side development frameworks with reactive, event sourcing and Actor pattern as basic theories. On top of this, developers can develop "distributed", "scale out", and "easy to test" application more simply.
CoreFX - The corefx repo contains the library implementation (called "CoreFX") for .NET Core. It includes System.Collections, System.IO, System.Xml and many other components.
CSLA .NET - business layer development framework https://cslanet.com/
Mono - Open source ECMA CLI, C#, F#, VB and .NET implementation
Mono-Addins - Mono.Addins is a generic framework for creating extensible applications, and for creating add-ins which extend those applications
peasy - Peasy is a middle tier framework that offers an easy to use and flexible rules engine and was designed to address common challenges such as concurrency handling, transactional support, fault tolerance, threading, scalability, async and multiple client support, and easy testability, all without a huge learning curve!
Plastic - Plastic provides encapsulation of things like Domain, Application Rules, Business Rules or Business Logic in Application. For this, Command pattern is used.
Signals - Signals is a .NET5 based framework which focuses on increasing the quality and productivity within development teams by providing them with tools, aspects and processes.
Spring.Net - Spring.NET is an open source application framework that makes building enterprise .NET applications easier
DotNetty - DotNetty is a port of Netty, asynchronous event-driven network application framework for rapid development of maintainable high performance protocol servers & clients.
AspectCore Framework - AspectCore Framework is an Aspect-Oriented Programming based cross platform framework for .NET Core and .NET Framework. Core support for aspect-interceptor,dependency injection integration , web applications , data validation , and more.
HopFramework - HopFramework is a framework to create projects easily applying Domain Driven Design and a lot of patterns to delivery a better solution.
Fusion - .NET Core and Blazor library that attempts to dramatically improve the way we implement real-time and high-load services by introducing a novel kind of "computed observables" - immutable, thread-safe, and most importantly, almost invisible for developers. Samples 1 Samples 2
silky - The Silky framework is designed to help developers quickly build a microservice development framework through simple code and configuration under the .net platform.

Application Templates

.NET Boxed Templates - .NET project templates with batteries included, providing the minimum amount of code required to get you going faster.
ASP.NET Core Starter Kit - backend: .NET Core, EF Core, C#; frontend: Babel, Webpack, React, CSS Modules
ProjectScaffold - A prototypical .NET solution recommended by the F# Foundation---includes file system setup, Paket for dependencies and FAKE for build/test automation. By default, build process also compiles documentation and generates NuGet packages.
Serene - Serenity is an ASP.NET MVC application platform designed to simplify and shorten development of data-centric business applications with a service-based architecture. Serene is a starter template to build Serenity applications.
Side-Waffle - Large collection of useful templates for Web and Desktop development.
Template10 - Windows 10 templates with design patterns.
Nucleus - Vue startup application template that uses ASP.NET Core API layered architecture at the back-end and JWT based authentication
JHipster.NET JHipster blueprint for replace orginal SpringBoot Backend by asp.net core. The main goal generator of jhipster is showcases best practices of modern web development in java. So the goal of the project is to do the same in .net. The Frontend can be generated with angular or react and soon with blazor.

Artificial Intelligence

AIMLBot (Program#) - A small, fast, standards-compliant yet easily customizable implementation of an AIML (Artificial Intelligence Markup Language) based chatter bot in C#.
SIML - Synthetic Intelligence Markup Language, a next generation Chatbot & Digital Assistant Language.
Mpt-Instruct-DotNet-S LLM that can generate and explain C# code (and its C# wrapper to run on consumer CPU with 5GB ram+, contains Console and Blazor sample projects)

Assembly Manipulation

Fody - Extensible tool for weaving .NET assemblies.
ILRepack - Open-source alternative to ILMerge.
Mono.Cecil - Cecil is a library to generate and inspect programs and libraries in the ECMA CIL form.

Assets

Cassette - Manages .NET web application assets (scripts, css and templates)
NodeAssets - Asset Manager for .NET that has live CSS updates using SignalR and can optionally leverage Node.js compilers
Bundle Transformer - Modular extension for Microsoft ASP.NET Web Optimization Framework. Its modules supports LESS, Sass, CoffeeScript, TypeScript, Mustache, Handlebars, Autoprefixer along with a bunch of different JS and CSS minifiers.
Bundler - Compile & Minify Less/Sass/Stylus/Css/JS/CoffeeScript/LiveScript files. Integrates with MVC and ServiceStack
SquishIt - Lets you easily bundle some CSS and JavaScript

Authentication and Authorization

ASP.NET Identity - New membership system for ASP.NET applications
ASP.NET SAML - SAML authentication support for ASP.NET apps
DotNetOpenAuth - A C# implementation of the OpenID, OAuth and InfoCard protocols
Logibit Hawk - A F# Hawk authentication library
IdentityModel - Helper library for identity & access control in .NET 4.5 and MVC4/Web API.
IdentityServer - Extensible OAuth2 and OpenID Connect provider framework.
OAuth - A very lightweight library for generating OAuth 1.0a signatures written in C#
Stuntman - Stuntman is a library for impersonating users during development leveraging .NET Claims Identity.
openiddict - Flexible and versatile OAuth 2.0/OpenID Connect stack for .NET

Blazor

BootstrapBlazor - A set of enterprise-class UI components based on Bootstrap and Blazor.
ant-design-blazor - A set of enterprise-class UI components based on Ant Design and Blazor WebAssembly.
MASA.Blazor - A set of enterprise-class UI components based on Material Design and Blazor WebAssembly.
Megabit.Blazorise - Blazorise is a component library built on top of Blazor and CSS frameworks like Bootstrap, Bulma and Material. Very easy to use.
blazork8s - k8s management ui in blazor and .NET Core.

Blockchain

Nethermind - full Ethereum client in .NET Core

Books

The Little ASP.NET Core Book - A free, open-source, tutorial-based book aiming to provide a simple introduction to ASP.NET Core.
.NET in Action, Second Edition - An introduction to implementing full-featured, cross-platform professional applications on the Microsoft .NET platform. [$]
.NET Maui in Action - A book about creating mobile and desktop apps using a common set of .NET tools. [$]
ASP.NET Core in Action, Third Edition - Build professional-grade full-stack web applications using C# and ASP.NET Core. [$]
ASP.NET Core Razor Pages in Action - A comprehensive guide to how to use Razor Pages to create dynamic websites that are easy to test and scale. [$]
ASP.NET Core Security - A practical and hands-on guide to securing web applications built with ASP.NET. [$]
ASP.NET Core Web API - A book about designing and implementing APIs using the REST and GraphQL standards. [$]
Blazor in Action - A guide to building UIs and client-side applications using C# and .NET. [$]
Building Web APIs with ASP.NET Core - Practical beginner’s guide to creating your first web APIs using ASP.NET Core. [$]
C# in Depth, Fourth Edition - deep dive into the details of the C# language. [$]
CLR via C#, Fourth Edition - Dig deep and master the intricacies of the common language runtime, C#, and .NET development. [$]
Code Like a Pro in C# - Build on your existing programming skills and upskill to professional-level C# programming. [$]
Dependency Injection in .NET - teaches you to use Dependency Injection to reduce hard-coded dependencies between application components in .NET. [$]
Entity Framework Core in Action - teaches how to use Entity Framework Core, including lighter weight data access alternatives such as Dapper. [$]
Functional Programming in C#, Second edition - Real world examples and practical techniques for functional programming in C# without the jargon and theory. [$]
Microservices in .NET Core, Second edition - A comprehensive guide to building microservice systems using the .NET stack. [$]
Pro .NET 5 Custom Libraries - Consists of sample projects for each data type implementation. Demonstrates implementation in C#. Covers dos and don'ts of each implementation. [$]
Pro .NET Benchmarking - Provides an in-depth look at software benchmarking for accurate performance measurement. Helps you get maximum performance impact by identifying and targeting the right bottlenecks. Includes coverage of the latest compilers and processors. [$]
Pro .NET Framework with the Base Class Library - Shows valuable tips and examples that reinforce the correct use of manage types, including how to avoid boxing/unboxing and better use of memory resources. [$]
Pro .NET Memory Management - Takes a deep dive into .NET memory management, including comprehensive coverage of how .NET memory works, implementation details, possible pitfalls, and ways to work around them. [$]
Pro ASP.NET Core 6 - The most comprehensive coverage available on ASP.NET Core 6 in full-color. Detailed explanations and plenty of working code to learn new functionality. Provides a fully functioning ASP.NET Core 6 application that can be used as a template for projects. [$]
Pro Microservices in .NET 6 - Shows you how to get up to speed with .NET 6, Docker, and microservices. Teaches you how to leverage microservice design patterns to strengthen an application. Provides environment options for orchestrators and Azure Kubernetes Service. [$]

Build Automation

Psake - .NET-based build automation tool written in PowerShell
FAKE - F# Make, a cross-platform build automation system
Invoke-Build - PowerShell build and test automation tool inspired by Psake.
MSBuild - The Microsoft Build Engine (MSBuild) is the build platform for .NET and Visual Studio
Cake - Cake (C# Make) is a cross-platform build automation system with a C# DSL.
Nake - Magic script-based C# task runner
Nuke - Cross-platform build automation system
FlubuCore - A cross platform build and deployment automation system for building projects and executing deployment scripts using C# code.

Business Intelligence

FastReport - The open source report generator for .NET Core 2.x/.Net Framework 4.x. FastReport can be used in ASP.NET MVC, Web API applications.
NReco PivotData - in-memory data aggregation/OLAP library, pivot tables generation (render to HTML, exports), ASP.NET pivot builder control [$][Free for single-deployment/non-SaaS]

Caching

CacheCow - An ASP.NET Web API HTTP caching implementation both on client and server
Akavache - An asynchronous, persistent key-value store
EasyCaching - A caching library that contains basic and some advanced usages of caching which can help handle caching more easier!
CacheManager - A common interface and abstraction layer for caching.
FastCache - 10X faster alternative to MemoryCache for .NET
Foundatio - A common interface with in memory, Redis and hybrid implementations.
Cashew - a .NET library for caching responses easily with an HttpClient through an API that is simple and elegant yet powerful.
Cache Tower - An efficient multi-layered caching system for .NET (In-Memory, Redis, Database, File etc)
FusionCache - An easy to use, high performance and robust cache with an optional distributed 2nd layer and some advanced features, like a fail-safe mechanism and advanced timeouts management
LazyCache - A simple, developer friendly, in-memory thread-safe caching service. It leverages Microsoft.Extensions.Caching and Lazy to provide performance and reliability in heavy load scenarios.

Calendar

iCal.NET iCal.NET is an iCalendar (RFC 5545) class library for .NET aimed at providing RFC 5545 compliance, while providing full compatibility with popular calendaring applications and libraries.

Chat

Stream Official .NET API client for Stream Chat, a service for building chat applications.

CLI

Appccelerate - Command Line Parser - A command-line parser with fluent definition syntax, different argument types, required and optional arguments, value restrictions, aliases, type conversion and semi-automatic usage help message composition
Argu - Declarative CLI argument & XML configuration parser for F# applications.
CliFx - Declarative framework for building command line interfaces.
Typin - Simple to use declarative framework for interactive CLI applications and command line tools (direct mode) that has its roots in CliFx.
clipr - A CLI library inspired by Python's argparse that transforms a command line into a strongly-typed object. It supports custom argument types, automated (and localized) help generation, and a variety of ways to store parsed arguments.
CliWrap - Wrapper for command line interfaces.
Colorful.Console - Colorful console output.
CommandDotNet - Model your console app using C# in a composable manner. Define commands with methods. Define subcommands with properties or nested classes. Extensible parsing and command execution.
Command Line Parser - The Command Line Parser Library offers to CLR applications a clean and concise API for manipulating command-line arguments and related tasks
CommandLineUtils - This is a fork of Microsoft.Extensions.CommandLineUtils, which is no longer under active development.
CsConsoleFormat - .NET C# library for advanced formatting of console output.
Docopt - Command-line interface description language that will make you smile.
EntryPoint - Composable CLI Argument Parser for .NET Core & .NET Framework 4.5+.
Fluent Command Line Parser - A simple, strongly typed .NET C# command-line parser library using a fluent easy to use interface
JustCli - That’s just a quick way to create your own command line tool.
Gui.cs - Terminal UI toolkit for .NET.
Power Args - PowerArgs converts command-line arguments into .NET objects that are easy to program against. It also provides a ton of optional capabilities such as argument validation, auto generated usage, tab completion, and plenty of extensibility
ReadLine - A GNU-Readline like library for .NET/.NET Core.
RunInfoBuilder - A unique command line parser, utilizing object trees for commands.
SharpNetSH - A simple netsh library for C#.
spectre.console - A library that makes it easier to create beautiful console applications.

CLR

Runtime - Mono and CoreCLR .NET runtimes, as well as the standard library and some higher level components like System.Linq and System.Text.Json.

CMS

Composite C1 - A web CMS that focus on UX and adaptability
mojoPortal - MojoPortal is an extensible, cross database, mobile friendly, web content management system (CMS) and web application framework written in C# ASP.NET
N2CMS - Open source, lightweight, code-first CMS able to seamlessly integrate into any MVC project.
Orchard - Free, open source, community-focused project aimed at delivering applications and reusable components on the ASP.NET platform
Piranha CMS - Piranha is the fun, fast and lightweight .NET framework for developing cms-based web applications with an extra bite. It's built on ASP.NET MVC and Web Pages and is fully compatible with both Visual Studio and WebMatrix. https://piranhacms.org
Umbraco - Umbraco is a free open source Content Management System built on the ASP.NET platform
DotNetNuke - DNN Platform is our free, open source web CMS and the foundation of every professional DNN solution. Over 750,000 organizations worldwide have built websites powered by the DNN Platform.
BlogEngine.NET - Simple but full featured ASP.NET blog
Squidex - Open source headless CMS and content management hub. https://squidex.io

Code Analysis and Metrics

.NET Compiler Platform ("Roslyn") Analyzers - A number of Roslyn diagnostic analyzers initially developed to help flesh out the design and implementation of the static analysis APIs.
PVS-Studio - PVS-Studio is a static analyzer on guard of code quality, security (SAST), and code safety. [Free for OSS] [$]
NDepend - is a Visual Studio and VS Team Services extension that estimates your .NET code quality and Technical-Debt, that lets create code rules with C# LINQ syntax, visualize code structure and focus on changes and evolution. [$]
App.Metrics - App Metrics is an open-source and cross-platform .NET library used to record and report metrics within an application and reports it's health. See the docs for me details.
CodeMaid - Visual studio extension to cleanup, dig through and simplify C#, C++, F#, VB, PHP, JSON, XAML, XML, ASP, HTML, CSS, LESS, SCSS, JavaScript and TypeScript coding.
StyleCop - StyleCop analyzes C# source code to enforce a set of style and consistency rules
Gendarme - Extensible rule-based tool to find problems in .NET applications and libraries
Metrics-Net - Capturing CLR and application-level metrics. So you know what's going on.
AspNet.Metrics - Capturing CLR, application-level web request metrics. Middleware and extensions using Metrics-Net
BenchmarkDotNet - Powerful .NET library for benchmarking.
Bencher - Suite of continuous benchmarking tools designed to catch performance regressions in CI.
Codinion - Enhanced syntax highlighting for C# and some other "Visual" features. [$]
NsDepCop - Static code analysis tool to enforce namespace dependency rules in C# projects.
WebBen - Is a tool for benchmarking your Hypertext Transfer Protocol (HTTP) server.

Code Snippets

.NET Fiddle - Write, compile and run C#, F# and VB code in the browser. The .Net equivalent of JSFiddle.
Sharplab - Run C# code using different branches and versions of Roslyn, see the IL that was produced and examine the JIT's output.

Compilers, Transpilers and Languages

ClojureCLR - A port of Clojure to the CLR, part of the Clojure project
F# - The F# compiler, core library and tools - a functional programming language for safer, faster, better code writing.
Hybridizer - CIL (C#, VB.Net, F#) to CUDA compiler. [$]
IronScheme - R6RS Scheme compiler, runtime and many standard libraries
JSIL - CIL to JavaScript Compiler http://jsil.org/
Mond - A dynamically typed scripting language written in C# with a REPL, debugger, and simple embedding API.
Mono-basic - Visual Basic Compiler and Runtime
Nemerle - Nemerle is a high-level statically-typed programming language for the .NET platform. It offers functional, object-oriented and imperative features. It has a simple C#-like syntax and a powerful meta-programming system.
Netjs - .NET to TypeScript and JavaScript compiler. Portable Class Libraries work great for this. You can even pass EXEs.
P - P is a language for asynchronous event-driven programming.
PeachPie - PeachPie is a PHP compiler and runtime for .NET and .NET Core, which allows entire PHP applications to run on the modern, secure and performant .NET and .NET Core platforms.
Roslyn - The .NET Compiler Platform ("Roslyn") provides open-source C# and Visual Basic compilers with rich code analysis APIs. It enables building code analysis tools with the same APIs that are used by Visual Studio.
Testura.Code - Wrapper around the Roslyn API and used for generation, saving and compiling C# code. It provides methods and helpers to generate classes, methods, statements and expressions.
VisualFSharp - The Visual F# compiler and tools
Fable - F# to JavaScript Compiler
LinqOptimizer - An automatic query optimizer-compiler for Sequential and Parallel LINQ
Roslyn-linq-rewrite - Compiles C# code by first rewriting the syntax trees of LINQ expressions using plain procedural code, minimizing allocations and dynamic dispatch.
Iron python - A python 2 implementation that is integrated with the dot net framework.
Amplifier.NET - Write and compile your own kernel function using C# and Amplifier will take care of running it on your favorite hardware. Amplifier allows .NET developers to easily run complex applications with intensive mathematical computation on Intel CPU/GPU, NVIDIA, AMD without writing any additional C kernel code.

Compression

SharpCompress - SharpCompress is a compression library for .NET/Mono/Silverlight/WP7 that can unrar, un7zip, unzip, untar unbzip2 and ungzip with forward-only reading and file random access APIs. Write support for zip/tar/bzip2/gzip are implemented
DotNetZip.Semverd - An open-source project that delivers a .NET library for handling ZIP files, and some associated tools. (fork of Unmaintained DotNetZip)
SharpZipLib - a Zip, GZip, Tar and BZip2 library written entirely in C# for the .NET platform
Snappy for Windows - Snappy compression library for .NET baked on P/Invoke
Snappy.Sharp - An implementation of Google's Snappy compression algorithm in C#.

Continuous Integration

TeamCity - Ready to work, extensible and developer-friendly build server — out of the box [$]
MyGet - Continuous Integration and Deployment, Hosted Package Repository for NuGet, NPM, Bower and VSIX [$]
AppVeyor - .NET Continuous Integration and Deployment as a service. [$] [Free for OSS]

Cryptography

BouncyCastle - Together with the .Net System.Security.Cryptography, the reference implementation for cryptographic algorithms on the CLR.
HashLib - HashLib is a collection of nearly all hash algorithms you've ever seen, it supports almost everything and is very easy to use
libsodium-net - libsodium for .NET - A secure cryptographic library
NaCl.Core - A managed-only cryptography library for .NET which provides modern cryptographic primitives.
Paseto.Core - A Paseto (Platform-Agnostic Security Tokens) implementation for .NET
Pkcs11Interop - Managed .NET wrapper for unmanaged PKCS#11 libraries that provide access to the cryptographic hardware
StreamCryptor - Stream encryption & decryption with libsodium and protobuf
SecurityDriven.Inferno - .NET crypto library. Professionally audited.
CryptoNet - .NET simple crypto library. Native c#.

Database

SliccDB - Lightweight Embedded (In-Memory) Graph Database for .net
RocksDB - C# binding for Facebook's RocksDB Key-Value store + native builds for Windows, macOS and Linux
BrightstarDb - BrightstarDB is a native .NET RDF triple store
DBreeze - DBreeze Database is an open-source embedded Key-Value store
Event Store - The open-source, functional database with Complex Event Processing in JavaScript
LiteDB - A .NET NoSQL Document Store in a single data file - https://www.litedb.org
RavenDB - A LINQ-enabled document database for .NET
Marten - PostgreSQL as a document database and event store for .NET applications
Realm Xamarin - A fast, easy-to-use alternative to SQLite & ORMs - https://realm.io/docs/dotnet/latest/
Streamstone - Event store for Azure Table Storage
StringDB - StringDB is a modular, key/value pair archival DB designed to consume tiny amounts of ram & produce tiny databases.
Ignite - Distributed in-memory platform: document database with SQL and LINQ support; distributed computations; distributed services and events.
Yessql - A .NET document database working on any RDBMS
JsonFlatFileDataStore - Simple JSON flat file data store with support for typed and dynamic data
Db4o-gpl - Object-oriented database, embedded and remote connections supported.
ZoneTree - Persistent, high-performance, transactional, and ACID-compliant ordered key-value database for .NET.

Database Drivers

MySQL Connector - Connector/Net is a fully-managed ADO.NET driver for MySQL
Npgsql - .NET data provider for PostgreSQL
MongoDB - Official MongoDB C# driver
RethinkDb.Driver - A RethinkDB database driver in C# striving for 100% ReQL API compatibility and completeness.
ServiceStack Redis - .NET's leading C# Redis client
StackExchange Redis - General purpose Redis client from StackExchange
Cassandra - DataStax .NET driver for Apache Cassandra
Couchbase - Official Couchbase .NET client library, based on the Enyim memcached client
Firebird.NET - The .NET Data provider is written in C# and provides a high-performance, native implementation of the Firebird API
FluentStorage - A polycloud .NET cloud storage abstraction layer originally known as Storage.Net. Provides a generic interface for Blob storage (AWS S3, GCP, FTP, SFTP, Azure Blob/File/Event Hub/Data Lake) and Messaging (AWS SQS, Azure Queue/ServiceBus).
Stowage - Bloat-free zero dependency .NET cloud storage kit that supports at minimum THE major cloud providers.

Datetime

NodaTime - Noda Time is an alternative date and time API for .NET. It helps you to think about your data more clearly, and express operations on that data more precisely. https://nodatime.org/
DateTimeExtensions - Common Date Time operations on the form of extensions to System.DateTime, including holidays and working days calculations on several culture locales.
Exceptionless.DateTimeExtensions - DateTimeRange, Business Day and various DateTime, DateTimeOffset, TimeSpan extension methods.

Decompilation

dnSpy - open-source .NET assembly browser, editor, decompiler and debugger
ILSpy - ILSpy is the open-source .NET assembly browser and decompiler
JustDecompile Engine - The decompilation engine of JustDecompile
dotPeek - Free-of-charge standalone tool based on ReSharper's bundled decompiler. It can reliably decompile any .NET assembly into equivalent C# or IL code. It can create Visual Studio solutions based on the original binary files in a straight-forward way. [Proprietary] [Free]

Deployment

Unfold - PowerShell-based deployment solution for .NET web applications
DbUp - .NET library that helps you to deploy changes to SQL Server databases. It tracks which SQL scripts have been run already, and runs the change scripts that are needed to get your database up to date
Octo Pack - Used to build NuGet packages of your application for deployment using tools such as Octopus Deploy
yuniql - Free and open source schema versioning and migration tool made with .NET Core. Run migrations with plain SQL, arrange versions in ordinary folders and seed your data from CSV via stand-alone CLI (no CLR needed), Azure Pipelines, Docker or ASP.NET Core code. https://yuniql.io

DirectX

Vortice.Windows - Cross platform .NET standard libraries for DirectX, WIC, Direct2D1, XInput, XAudio and X3DAudio

Distributed Computing

.NEXT Raft - Raft implementation for .NET and ASP.NET Core that allows to build clustered microservices powered by distributed consensus and replication
Orleans - Orleans is a framework that provides a straight-forward approach to building distributed high-scale computing applications, without the need to learn and apply complex concurrency or other scaling patterns. It was created by Microsoft Research.
Orleankka - Orleankka is a functional API for Microsoft Orleans framework. It is highly suitable for scenarios where having composable, uniform communication interface is preferable, such as: CQRS, event-sourcing, re-routing, FSM, etc. Additional API available for F# called Orleankka.FSharp.
Akka.net - Akka.NET is a port of the popular Java/Scala framework Akka to .NET. This is a community-driven port and is not affiliated with Typesafe who makes the original Java/Scala version.
Zebus - Zebus is a lightweight, highly versatile, peer-to-peer service bus, built with CQRS principles in mind. It allows applications to communicate with each other in a fast and easy manner. Most of the complexity is hidden in the library and you can focus on writing code that matters to you, not debugging messaging code. A very fundamental base for any distributed application.
FsShelter - F# library for authoring Apache Storm components and topologies. Offering high-level abstractions for distributed and fault-tolerant event stream processing.
Foundatio - Pluggable foundation blocks for building distributed apps.
MBrace - Integrated Data Scripting for the Cloud
protoactor-dotnet - Proto Actor - Ultra fast distributed actors for Golang and C#

DLR

cmd - C# library to run external programs in a simpler way. Demonstration of "dynamic" features of C#.

Documentation

Sandcastle - Sandcastle Help File Builder similar to NDoc
SourceBrowser - Source browser website generator that powers https://referencesource.microsoft.com
Swashbuckle - Seamlessly adds a Swagger to Web API projects.
F# Formatting - Tools for documenting F# and C# projects from F# script files, Markdown documents and inline XML or Markdown comments
DocFX - Tools for building and publishing API documentation for .NET projects
DocNet - Your friendly static documentation generator, using markdown files to build the content.

E-Commerce and Payments

Paypal Merchant SDK - Official PayPal Merchant SDK for .NET
NopCommerce - nopCommerce. Free open-source e-commerce shopping cart (ASP.NET Core)
ServiceStack.Stripe - Typed .NET clients for stripe.com REST APIs
SmartStoreNET - Free ASP.NET MVC e-commerce Shopping Cart Solution
Stripe.Net - Stripe.net is a full service .NET API for https://stripe.com/
Virto Commerce - Virto Commerce is the second generation release and is the only enterprise level e-commerce product fully available under Open Source license. Virto Commerce is based on .NET 4.5 with extensive use of MVC, IoC, EF, Azure, AngularJS and many other cutting edge technologies. It can be deployed in Microsoft Cloud (Azure), Amazon Web Services (AWS) and on-premise. https://virtocommerce.com
SimplCommerce - Super simple ecommerce system built on .NET Core. Simple to use and easy to customize. Thanks to .NET Core, you can run the SimplCommerce on Windows, Linux. With various RDBMS: Microsoft SQL Server, PostgreSQL, MySQL
GrandNode - Headless, multi-vendor, multi-tenant, the most advanced open source e-commerce platform based on .NET Core 5.0 and MongoDB.
Square - The official SDK for Square payments and other Square APIs.
Adyen - The official Adyen Payment API Library for .NET

Emulators

Blzhawk - BizHawk is a multi-system emulator written in C#. BizHawk provides nice features for casual gamers such as full screen, and joypad support in addition to full rerecording and debugging tools for all system cores.
Ryujinx - Experimental Nintendo Switch Emulator written in C#

Environment Management

Dotnet CLI - The cross-platform .NET Core command-line toolchain utility.

ETL

Cinchoo ETL - ETL Framework for .NET (Read / Write CSV, Flat, Xml, JSON, Key-Value formatted files)
Reactive ETL - Reactive ETL is a rewrite of Rhino ETL using the reactive extensions for .NET

Event aggregator and messenger

Mediator.Net - A simple mediator for .NET for sending command, publishing event and request response with pipelines supported
MediatR - Simple, unambitious mediator implementation in .NET
Rx Event Aggregator - Super-simple Reactive-Extension code from Reactive.EventAggregator
TinyMessenger - A lightweight event aggregator/messenger for loosely coupled communication.
Xer.Cqrs - A simple library for creating applications based on the CQRS pattern with support for attribute routing and hosted handlers. Developed in C# targeting .NET Standard 1.0.
FluentMediator - FluentMediator is an unobtrusive library that allows developers to build custom pipelines for Commands, Queries and Events
EventFlow - EventFlow is an Async/await first CQRS and Event Sourcing DDD framework for .NET

Exceptions

Exceptionless - Exceptionless .NET Client

Extensions

ExtensionMethods.Net - Site with collection of extension methods
Z.ExtensionMethods - Over a 1000 useful extension methods

Functional programming

Curryfy - Provides strongly typed extensions methods for C# delegates to take advantages of functional programming techniques, like currying and partial application.
language-ext - This library uses and abuses the features of C# 6+ to provide a functional 'Base class library', that, if you squint, can look like extensions to the language itself. It also includes an 'Erlang like' process system (actors) that can optionally persist messages and state to Redis (note you can use it without Redis for in-app messaging). The process system additionally supports Rx streams of messages and state allowing for a complete system of reactive events and message dispatch.
Optional - A robust option type for C#
JFlepp.Maybe - A Maybe type for C#, aimed as an idiomatic port of the option type in F# to C#
Optuple - .NET Standard Library for giving (bool, T) Option-like semantics in a non-obtrusive way; this is, there is no new option type dependency for a library or its users.
MoreLinq - Provides extra methods to LINQ to Objects.

Game

MonoGame - One framework for creating powerful cross-platform games
FNA - FNA is an XNA4 reimplementation that focuses solely on developing a fully accurate XNA4 runtime for the desktop
CocosSharp - CocosSharp is a C# implementation of the Cocos2D and Cocos3D APIs that runs on any platform where MonoGame runs
Duality - Duality is a 2D game development framework. Focused on modularity, comes with a visual editor.
Stride Game Engine - Stride Game Engine is a 2D/3D cross-platform game engine featuring a scene editor, particles, physically based rendering (PBR), scripting, and much more
Wave Engine - Wave engine is a free C# component-based modern game engine which allows you to create cross-platform games supporting Kinect, Oculus Rift, Vuforia, Cardboard, Leap Motion and much more. [Free][Proprietary]
UrhoSharp - UrhoSharp is a C# implementation of the Urho3D game engine that runs on iOS, Mac, Windows, Android and Linux systems
Nez - Nez is a free 2D-focused framework that works with MonoGame and FNA
BEPUphysics - BEPUphysics is a pure C# 3D physics library
Devtodev - A full-cycle analytics solution for game developers.
UnrealCLR - Unreal Engine .NET Core integration
osu!framework - A 2D application/game written with amazing games in mind.

GIS

NetTopologySuite A .NET GIS solution that is fast and reliable for the .NET platform
SharpMap An easy-to-use mapping library for use in web and desktop applications
OsmSharp - C# library to work with OpenStreetMap (OSM) data. Provides reading, writing and route-planning for OSM data.
GeoJSON4EntityFramework - A library to create GeoJSON from Entity Framework Spatial Data or Well-Known Text (WKT) inputs.
GeoJSON.NET - .Net library for GeoJSON types & corresponding Json.Net (de)serializers
CoordinateSharp - Easily parse or convert coordinate formats and calculate location based solar/lunar information.
DEM Net Elevation API - .Net library for Digital Elevation Models, allows 3D terrain generation in glTF / STL format.

Git Tools

Husky.Net - Git hooks made easy with Husky.Net internal task runner, You can use it to lint your commit messages, run tests, lint code, etc... when you commit or push. supports C# scripts, gitflow hooks, Multiple file states (staged, lastCommit, glob)
Bonobo Git Server - Bonobo Git Server for Windows is a web application you can install on your IIS and easily manage and connect to your Git repositories. https://bonobogitserver.com/
GitExtensions - GitExtensions is a shell extension, a Visual Studio 2008/2010/2012/2013 plugin and a standalone Git repository tool. https://gitextensions.github.io/
GitLink - let's users step through their code hosted on GitHub or BitBucket
GitVersion - Generate a Semantic Version Number based on the state of your Git repository
LibGit2Sharp - LibGit2Sharp brings all the might and speed of libgit2, a native Git implementation, to the managed world of .NET and Mono.
GitRead.Net - GitRead.Net is a .NET Standard library which allows you to very easily interrogate a Git repository that you have on disk. It allows you to enumerate the commit log, count lines per file and list files changed by a commit.
NGit - NGit is a port of JGit to C#
posh-git - A PowerShell environment for Git
RepoZ - A Git repository information aggregator with Windows Explorer & CLI-enhancements
Git Credential Manager for Windows - Helps solving issues of credentials, made by Microsoft

Graphics

LibTessDotNet - .NET port of the famous GLU Tessellator, triangulates polygons
Oxyplot - OxyPlot is a cross-platform plotting library for .NET
OpenTK - The Open Toolkit is an advanced, low-level C# library that wraps OpenGL, OpenCL and OpenAL
NGraphics - NGraphics is a cross-platform library for rendering vector graphics on .NET
Aspose.Drawing - Fully managed, cross-platform, complete 2D graphic library for drawing text, geometries, and images, with System.Drawing compatible API. [$]
ScottPlot - A plotting library to interactively displays large datasets. Line plots, bar charts, pie graphs, scatter plots, and more. It supports WinForms, WPF, Avalonia, Console.
LiveCharts2 - Simple, flexible, interactive & powerful charts, maps, and gauges for .Net. LiveCharts2 supports WPF, WinForms, Xamarin, Avalonia, WinUI, UWP.
Helix Toolkit - Helix Toolkit is a collection of 3D components for .NET
AssimpNet - A cross-platform .NET Standard wrapper for the Open Asset Importer ("Assimp"). The library enables importing, processing, and exporting of 3D models for rendering in graphics/game applications. Over 40 formats are supported for importing (e.g. OBJ, FBX, GLTF, 3DS, Collada) and a subset of those formats can be exported to (e.g. OBJ, GLTF, 3DS, Collada). Mesh processing features allow for mesh data to be generated or optimized for real-time rendering.
Silk.NET - A cross-platform, high-performance, low-level .NET Standard wrapper for many advanced APIs such as OpenGL, OpenCL, OpenAL, OpenXR, Assimp, GLFW, as well as many others. In addition to wrapping over Native APIs, it also comes with its own Windowing and Input abstraction. This makes game and application development with Silk.NET a breeze, and has pretty much everything a 3D application developer would need.
Veldrid - A low-level, portable graphics and compute library for .NET
RealTimeGraphX - RealTimeGraphX is a data type agnostic, high performance plotting library for WPF, UWP and soon, Xamarin Forms.
VectSharp - .NET library to create vector graphics and text, and then export it to PDF, SVG and raster image formats.

GraphQL

GraphQL.NET - Implementation of Facebook's GraphQL in .Net
HotChocolate - GraphQL server compatible to all GraphQL compliant clients like Strawberry Shake, Relay, Apollo Client, and various other clients and tools.
graphql-net - GraphQL to IQueryable for .NET.
EntityGraphQL - library to build a GraphQL API on top of data model with the extensibility to easily bring multiple data sources together in the single GraphQL schema (EF is not a requirement - any ORM working with LinqProvider or an in-memory object will work).
ZeroQL - high-performance C#-friendly GraphQL client. It supports Linq-like syntax. It doesn't require Reflection.Emit or expressions. As a result, the runtime provides performance very close to a raw HTTP call.

GUI

HandyControl - Contains some simple and commonly used WPF controls
Lara - Lara Web Engine is a library for developing Web user interfaces in C#
QtSharp - Mono/.NET Bindings for Qt
Qml.Net - A cross-platform Qml/.NET integration for Mono/.NET/.NET Core
MahApps.Metro - Toolkit for creating Metro-styled WPF apps
Callisto - A control toolkit for Windows 8 XAML applications. Contains some UI controls to make it easier to create Windows UI style apps for the Windows Store in accordance with Windows UI guidelines.
ObjectListView - ObjectListView is a C# wrapper around a .NET ListView. It makes the ListView much easier to use and teaches it some new tricks
DockPanelSuite - The Visual Studio inspired docking library for .NET WinForms
AvalonEdit - The WPF-based text editor component used in SharpDevelop
XWT - A cross-platform UI toolkit for creating desktop applications with .NET and Mono
Gtk# - Gtk# is a Mono/.NET binding to the cross platform Gtk+ GUI toolkit and the foundation of most GUI apps built with Mono
MaterialDesignInXamlToolkit - Toolkit for creating Material Design styled WPF apps
Eto.Forms - Cross-platform GUI framework for desktop and mobile applications in .NET and Mono
Dragablz - Dragable, tearable WPF tab control (similar to Chrome) which supports layouts and is full themeable, including themese compatible with MahApps and Material Design.
Fluent.Ribbon - Fluent Ribbon Control Suite is a library that implements an Office- and Windows 8-like Ribbon for WPF.
Office Ribbon - A library that implements MS Office Ribbon for WinForms.
MaterialSkin - Theming .NET WinForms, C# or VB.Net, to Google's Material Design principles.
Xamarin.Forms - Build native UIs for iOS, Android and Windows from a single, shared C# codebase.
SciterSharp - Create .NET cross-platform desktop apps using not just HTML, but all features of Sciter engine: CSS3, SVG, scripting, AJAX, <video>... Sciter is free for commercial use
Empty Keys UI - Multi-platform and multi-engine XAML based user interface library [Free][Proprietary]
UWP Community Toolkit - The UWP Community Toolkit is a collection of helper functions, custom controls, and app services. It simplifies and demonstrates common developer tasks building UWP apps for Windows 10.
ScintillaNET - Windows Forms control for the Scintilla text editor component (Scintilla is used by Notepad++)
FastColoredTextBox - Fast Colored TextBox is text editor component for .NET. Allows you to create custom text editor with syntax highlighting. It works well with small, medium, large and very-very large files.
Avalonia - A multi-platform .NET UI framework (formerly known as Perspex).
Modern UI for WPF - MUI - Set of controls and styles to convert WPF applications into a great looking Modern UI apps.
WinApi - A simple, direct, ultra-thin CLR library for high-performance Win32 Native Interop with automation, windowing, DirectX, OpenGL and Skia helpers.
Neutronium - Build .NET desktop applications using HTML, CSS, javascript and MVVM bindings such as with WPF.
Ooui - A small cross-platform UI library that brings the simplicity of native UI development to the web
AdonisUI - Lightweight UI toolkit for WPF applications offering classic but enhanced Windows visuals.
Windows UI Library - The Windows UI Library (WinUI) provides official native Microsoft UI controls and features for Windows UWP apps.
Bunifu UI Framework - Carefully crafted Winforms controls and components for creating stunning modern application UI. [$]
Ookii.Dialogs.Wpf - Enable WPF applications to access common Windows dialogs such as task dialogs, credential dialog, progress dialog, folder browser dialog, and more
Ookii.Dialogs.WinForms - Enable Windows Forms applications to access common Windows dialogs such as task dialogs, credential dialog, progress dialog, folder browser dialog, and more
UNO Platform - The only platform for building native mobile, desktop and WebAssembly with C#, XAML from a single codebase. Open source and professionally supported. Website: platform.uno

HTML and CSS

AngleSharp - Complete HTML5 DOM and CSS3 OM construction
dotless - .NET port of the Ruby Less CSS lib http://www.dotlesscss.org
ExCSS - CSS3 parser library for C#
HtmlAgilityPack - an agile HTML parser that builds a read/write DOM and supports plain XPath or XSLT
LibSass Host - .NET wrapper around the libSass library with the ability to support a virtual file system
LtGt - lightweight HTML processor, can be used to parse and navigate DOM, handles CSS selectors, can convert to Linq2Xml, easily extensible, and more.

HTTP

Tiny.RestClient - Simpliest Fluent REST client for .NET.
Http.fs - A functional HTTP client for F#.
RestSharp - Simple REST and HTTP API client for .NET
Flurl - Fluent, portable, testable REST/HTTP client library
EasyHttp - HTTP library for C#
Refit - The automatic type-safe REST library for Xamarin and .NET
RestEase - Easy-to-use typesafe REST API client library, which is simple and customisable. Heavily inspired by Refit
RestLess - The automatic type-safe-reflectionless REST API client library for .Net Standard.
HttpClientGoodies - utilities for working with HttpClient
WebApiClient An open source project based on the HttpClient. You only need to define the c# interface and modify the related features to invoke the client library of the remote http interface asynchronously.
Apizr Refit based web api client, but resilient (retry, connectivity, cache, auth, log, priority, etc...).

IDE

AvalonStudio - An extensible, cross platform IDE written in C# for Embedded C/C++, .NET Core, Avalonia and Typescript
SharpDevelop - A free IDE for .NET programming languages
MonoDevelop - MonoDevelop is a cross-platform IDE mostly aimed at Mono/.NET developers
Visual Studio Express - The free lightweight version of Visual Studio for .NET programming.
Visual Studio Community - A full-featured IDE
Waf DotNetPad - A simple and fast code editor that makes fun program with C# or Visual Basic.
Visual Studio Code - Excellent open source editor from Microsoft, based on Electron.
Ionide - An Atom Editor and Visual Studio Code package suite for cross platform F# development.
Rider - A cross-platform C# IDE based on the IntelliJ platform and ReSharper
RoslynPad - A simple C# editor based on Roslyn and AvalonEdit.
Consulo - A cross-platform IDE with C# & Java support, fork of IntelliJ IDEA Community Edition
vvvv A visual live-programming environment for .NET [Free for OSS]
- CSharp Analyzer by MongoDB A free Visual Studio Extension for MongoDB users, helping translate your code into MongoDB queries

Image Processing

ImageWizard - Image processing webservice based on ASP.NET Core and ImageSharp / SkiaSharp / SvgNet / DocNET
ImageResizer - Add commands to image URLs to get altered versions in milliseconds. Resizing, editing etc of images in real-time.
ImageProcessor - Open-source .NET library to manipulate images on-the-fly.
ImageSharp - Fully managed cross-platform library for processing of image files.
MagicScaler - High-performance image processing pipeline for .NET, focused on making complex imaging tasks simple.
DynamicImage - High-performance open-source image manipulation library for ASP.NET.
MetadataExtractor - Extracts Exif, IPTC, XMP, ICC and other metadata from image files.
Emgu CV - Cross-platform .NET wrapper for the OpenCV library.
SimpleITK - A simplified path to Insight. Open-source multi-dimensional image analysis in Python, R, Java, C#, Lua, Ruby, TCL and C++. Developed by the Insight Toolkit community for the biomedical sciences and beyond.
DotImaging - Minimalistic .NET imaging portable platform
Magick.NET - .NET wrapper for the ImageMagick library.
OpenCvSharp - Cross platform wrapper of OpenCV for .NET Framework.
PixelViewer - Cross-platform (Windows/macOS/Linux) image viewer which supports reading raw Luminance/YUV/RGB/ARGB/Bayer pixels data from file and rendering it. 10/16-bit YUV and viewing image frame sequence are also supported (v1.99+).
TeximpNet - A cross-platform .NET Standard library for reading/manipulating/writing image files. The primary focus is to create 2D/3D/Cubemap textures for graphics/game applications, notably to convert images to GPU compressed formats and generate mipmaps. The library wraps the FreeImage native library to import/export over 30 common image formats, and wraps the Nvidia Texture Tools native library for GPU compression features. It also has a fully featured DDS format importer/exporter written in C#.
Colourful - Open source .NET library for working with color spaces.
Imgix-CSharp - Easily update image urls to be fast and responsive. [$]
ColorHelper - Useful methods for work with colors.

Install tools

Wix Toolset - The most powerful set of tools available to create your Windows installation experience
Squirrel - Squirrel is both a set of tools and a library, to completely manage both installation and updating your desktop Windows application.
Chocolatey - like yum or apt-get, but for Windows.
Wax - An interactive editor for WiX projects.
Onova - An unopinionated auto-update framework for desktop applications.

Interactive programming

.NET Interactive - .NET Interactive takes the power of .NET and embeds it into your interactive experiences.

Internationalization

i18n - Smart internationalization for ASP.NET MVC
MessageFormat.NET - ICU MessageFormat implementation in .NET lets you write contextual UI messages (PCL library)
ResX Resource Manager - The most popular free tool to localize all kind of applications with resx-based resources.

Interoperability

CppSharp - Tools to surface C++ APIs to C#
Sharpen - Sharpen is an Eclipse plugin created by db4o that allows you to convert your Java project into C#
CXXI - C++ interop framework
pythonnet - Python and .NET interop framework
PInvoke Interop Assistant - Converts C to managed P/Invoke signatures or verse visa.
pinvoke - A library containing P/Invoke code for latest Windows OS.
LegacyWrapper - LegacyWrapper uses a wrapper process to call DLLs from a process of the opposing architecture (x86 or AMD64).
Pyrolite - This library allows your Java or .NET program to interface very easily with the Python world. It uses the Pyro protocol to call methods on remote objects.

IoC

Castle Windsor - Castle Windsor is best of breed, mature Inversion of Control container available for .NET and Silverlight
Unity - Lightweight extensible dependency injection container with support for constructor, property, and method call injection
Autofac - An addictive .NET IoC container
DryIoc - Simple, fast all fully featured IoC container.
Ninject - The ninja of .NET dependency injectors
Spring.Net - Spring.NET is an open source application framework that makes building enterprise .NET applications easier
Lamar - A fast IoC container heavily optimized for usage within ASP.NET Core and other .NET server side applications.
LightInject - A ultra lightweight IoC container
Simple Injector - Simple Injector is an easy-to-use Dependency Injection (DI) library for .NET 4+ that supports Silverlight 4+, Windows Phone 8, Windows 8 including Universal apps and Mono.
Microsoft.Extensions.DependencyInjection - The default IoC container for NET applications.
Scrutor - Assembly scanning extensions for Microsoft.Extensions.DependencyInjection.
VS MEF - Managed Extensibility Framework (MEF) implementation used by Visual Studio.
TinyIoC - An easy to use, hassle free, Inversion of Control Container for small projects, libraries and beginners alike.
Stashbox - A lightweight, portable dependency injection framework for .NET based solutions.

JavaScript Engines

ClearScript - A library that makes it easy to add scripting to your .NET applications. It currently supports JavaScript (via V8 and JScript) and VBScript.
Edge.js - Run .NET and Node.js code in-process on Windows, macOS, and Linux
Jint - JavaScript interpreter for .NET which provides full ECMA 5.1 compliance and can run on any .NET platform.
Jurassic - A implementation of the ECMAScript language and runtime. It aims to provide the best performing and most standards-compliant implementation of JavaScript for .NET.
YantraJS - JavaScript Runtime (Similar to NodeJS) for .NET Standard, compiles JavaScript to IL, support for many ES6 features, generators, CommonJS modules, CSX modules and expression compiler.

Logging

Essential Diagnostics - Extends the inbuilt features of System.Diagnostics namespace to provide flexible logging
NLog - NLog - Advanced .NET and Silverlight logging
Logazmic - Open source NLog viewer for Windows
ELMAH - Official ELMAH site
Elmah MVC - Elmah for MVC
Logary - Logary is a high performance, multi-target logging, metric, tracing and health-check library for Mono and .NET. .NET's answer to DropWizard. Supports many targets, built for micro-services.
Log4Net - The Apache log4net library is a tool to help the programmer output log statements to a variety of output targets
Rollbar.NET - Simplifies real-time remote error monitoring while using Rollbar.com. Open-source Rollbar Notifier SDK for any .NET-based technology stack. The SDK that can be used in any application built on the following .NET versions: .NET Core 2.0+, .NET Standard 2.0+, .NET Full Framework 4.5.1+, Mono, Xamarin, and, in general, any implementation of the .NET Standard 2.0+. It simplifies building data payloads based on exception data, tracing data, informational messages, and telemetry data and sends the payloads to the Rollbar API for remote monitoring and analysis of the hosting application's behavior.
Sejil - Capture, view and filter your ASP.NET Core app's logs right from your app. It supports structured logging, querying as well as saving log queries.
Sentry - .NET SDK for Sentry Open-source error tracking that helps developers monitor and fix crashes in real time..
Serilog - A no-nonsense logging library for the NoSQL era. Combines the best of traditional and structured diagnostic logging in an easy-to-use package.
StackExchange.Exceptional - Error handler used for the Stack Exchange network
Semantic Logging Application Block (SLAB) - Extends the inbuilt features of System.Diagnostics.Tracing namespace (EventSource class) to log to several sinks including Azure Tables, Databases, files (JSON, XML, text). Supports in-process and out-of-process logging through ETW, and Rx for real-time filtering/aggregating of events.
ULogViewer - Cross-Platform (Windows/macOS/Linux) Universal Log Viewer which supports reading and parsing various type of logs. You can also define your own profile to parse and show logs.
Foundatio - A fluent logging API that can be used to log messages throughout your application.
Exceptionless - Exceptionless .NET Client
Loupe - Centralized .NET logging and monitoring. [Proprietary] [Free Tier]
elmah.io - Cloud logging for .NET web applications using ELMAH. Find bugs before you go live. Powerful search, API, integration with Slack, GitHub, Visual Studio and more. [Free for OSS] [$]
BugSnag - Logs errors. Includes useful diagnostic info like stack trace, session, release, etc. Has a free tier. [Free for OSS][$]
ZeroLog - ZeroLog is a zero-allocation .NET logging library. It provides basic logging capabilities to be used in latency-sensitive applications, where garbage collections are undesirable.

Machine Learning and Data Science

Infer.NET - A framework for running Bayesian inference in graphical models. It can also be used for probabilistic programming.
Accord.NET - Machine learning framework combined with audio and image processing libraries (computer vision, computer audition, signal processing and statistics).
Accord.NET Extensions - Advanced image processing and computer vision algorithms made as fluent extensions.
AForge.NET - Framework for developers and researchers in the fields of Computer Vision and Artificial Intelligence (image processing, neural networks, genetic algorithms, machine learning, robotics).
Catalyst Cross-platform Natural Language Processing (NLP) library inspired by spaCy, with pre-trained models, out-of-the box support for training word and document embeddings, and flexible entity recognition models. Part of the SciSharp Stack
Deedle - Data frame and (time) series library for exploratory data manipulation with C# and F# support
FsLab - A collection of data science and machine learning libraries for F# and .NET
GeneticSharp - Multi-platform genetic algorithm library for .NET Core and .NET Framework. The library has several implementations of GA operators, like: selection, crossover, mutation, reinsertion and termination.
numl - Designed to include the most popular supervised and unsupervised learning algorithms while minimizing the friction involved with creating the predictive models.
ML.NET - Cross-platform open-source machine learning framework which makes machine learning accessible to .NET developers.
R Provider - Type provider that exposes R packages and functions in a type-safe way to F# callers
F# Data - F# type providers for accessing XML, JSON, CSV and HTML files (based on sample documents) and for accessing WorldBank data
Spreads - Series and Panels for Real-time and Exploratory Analysis of Data Streams. Spreads library is optimized for performance and memory usage. It is several times faster than other open source projects.
SciSharp STACK - A rich machine learning ecosystem for .NET created by porting the most popular Python libraries to C#.
Synapses - An in-memory neural network library written in F#.
m2cgen - A CLI tool to transpile trained classic ML models into a native .NET (C#, F# or Visual Basic) code with zero dependencies.

Markdown Processors

MarkdownSharp - Open source C# implementation of Markdown processor, as featured on Stack Overflow.
F# Formatting - Tools for documenting F# and C# projects. The library contains extensible Markdown parser as a core component.
CommonMark.NET - Implementation of CommonMark specification in C# for converting Markdown documents to HTML. Optimized for maximum performance and portability.
markdig - A fast, powerful, CommonMark compliant, extensible Markdown processor for .NET.

Mail

FluentEmail - A fluent wrapper for System.Net.Mail with Razor templating support.
MailKit - A complete cross-platform mail stack including IMAP, POP3, SMTP, authentication and more. Built on top of MimeKit.
MailKitSimplified - A fully-featured fluent wrapper for MailKit that makes sending and receiving emails as simple as possible.
MimeKit - A cross-platform .NET MIME creation and parser library with support for S/MIME, PGP, TNEF and Unix mbox spools.
PreMailer.Net - C# library that moves your stylesheets to inline style attributes, for maximum compatibility with e-mail clients.
StrongGrid - Client for SendGrid's v3 API. Not only allows you to send emails, but also allows you to bulk import contacts, manage lists and segments, create custom fields for your lists, etc. Also includes a parser for SendGrid Webhooks.

Mathematics

MathNet - Math.NET is an open source initiative to build and maintain toolkits covering fundamental mathematics, targeting advanced but also every day needs of .NET developers
Microsoft Automatic Graph Layout - A set of tools for graph layout and viewing.
UnitConversion - Expansible Unit Conversion Library for .NET Core and .NET Framework
ALGLIB - ALGLIB is a cross-platform numerical analysis and data processing library. It supports several programming languages (C++, C#, Delphi) and several operating systems (Windows and POSIX, including Linux) [Proprietary] and [Free Edition]
AutoDiff - AutoDiff is a library for quickly computing gradients of functions defined by expressions. Mainly useful in numerical optimization
GeometRi - Simple and lightweight computational geometry library for .Net
Rationals - Implementation of rational number arithmetic for .NET with arbitrary precision.
MKL.NET - A simple cross platform .NET API for Intel MKL.
AngouriMath - An open-source symbolic/computer algebra library, made primarily for C# and F#. It covers a range of features and might be considered as an alternative to SymPy in .NET.
Vim.Math3d - A feature-rich cross-platform replacement for System.Numerics with support for consistent serialization and binary layout, and additional structures and algorithms for efficient 3D Math.
WPF-Math - a .NET library for rendering mathematical formulae using the LaTeX typesetting style, for the WPF framework
Jodo.Numerics - Provides extra number types (such as fixed-point and non-overflowing numbers) with full support for operators, math, string-parsing etc. Extensively tested, and cross-platform compatible.

Media

CSCore - An advanced audio library, supporting playback/recording, decoding/encoding and processing of audio data in realtime (effects, visualizations, ...).
TagLib# - TagLib# (aka taglib-sharp) is a library for reading and writing metadata in media files, including video, audio, and photo formats
LibVLCSharp - Xamarin bindings for libvlc, the multimedia framework powering the VLC applications made by VideoLAN.
NAudio - Playback, decode and encode audio in a variety of file formats such as MP3, MP4, WAV, AIFF, Speex, etc.
Xabe.FFmpeg - .NET Standard wrapper for FFmpeg. It allows to process media without know how FFmpeg works, and can be used to pass customized arguments to FFmpeg from C# application. [$]
SeeShark - Cross-platform camera library for .NET using FFmpeg supporting over 190 pixel formats

Metrics

C# StatsD Client - C# client for Etsy's StatsD
Foundatio - A common interface with in-memory, Redis, StatsD, and Metrics.NET implementations.

Micro Framework

.NET Micro Framework Interpreter - Microsoft® .NET Micro Framework (NETMF) for developing embedded applications on small devices using Visual Studio

Minification

Microsoft Ajax Minifier - Contains JS and CSS minifiers which have a highest performance, because its have been specifically designed for .NET. Optionally produce Source Maps for JS code.
Web Markup Minifier - .NET library that contains a set of markup minifiers. The objective of this project is to improve the performance of web applications by reducing the size of HTML, XHTML and XML code.
CompressedStaticFiles - Send compressed static files to the browser without having to compress on demand, also has support for sending more advanced image formats when the browser indicates that i has support for it.

Misc

CSharp Pad - A web-based C# REPL with awesome code completion.
AzureCrawler - Take HTML Snapshots for your Angular, Ember, Durandal or any JavaScript applications
CSScript - CS-Script is a CLR based scripting system which uses C# as a programming language. CS-Script currently targets Microsoft implementation of CLR (.NET 2.0/3.0/3.5/4.0/4.5) with full support on Mono. Comes with many additional features, such as script hosting.
CsvHelper - Library to help reading and writing CSV files JoshClose/CsvHelper
RecordParser - Library to help reading and writing CSV and Flat files with zero heap allocation.
Hashids.net - Generate short unique ids from integers, as per https://hashids.org
ConsoleTableExt - Fluent library to create table for .Net console application.
FlatMapper - A library to import and export data from and to plain text files in a LINQ-compatible way.
FluentValidation - A small validation library for .NET that uses a fluent interface and lambda expressions for building validation rules.
FormHelper - Form & Validation Helper for ASP.NET Core. Form Helper helps you to create ajax forms and validations without writing any javascript code. (Compatible with Fluent Validation)
Guard - A high-performance, extensible argument validation library.
Valit - Valit is dead simple, fluent validation for .NET Core.
Validot - Validot is a performance-first, compact library for advanced model validation. Using a simple declarative fluent interface, it efficiently handles classes, structs, nested members, collections, nullables, plus any relation or combination of them. It also supports translations, custom logic extensions with tests, and DI containers.
Humanizer - Humanizer meets all your .NET needs for manipulating and displaying strings, enums, dates, times, timespans, numbers and quantities
LINQPad - a C#/VB/F# scratchpad that instantly executes any expression, statement block or program with rich output formatting and a wealth of features. Also lets you interactively query databases in LINQ. [$]
LINQPad.QueryPlanVisualizer - View SQL Server and Postgres query plans directly inside LINQPad.
Polly - Express transient-exception-handling and resilience policies such as Retry, Wait-and-Retry, Circuit Breaker, and Bulkhead Isolation in a fluent manner. Fully thread-safe and full async support. (4.0 / 4.5 / .NET Core / .NET Standard / Xamarin).
Rant - The Rant Procedural Text Generation DSL
ScriptCS - Write C# apps with a text editor, NuGet and the power of Roslyn!
Shielded - Software Transactional Memory (STM) implementation for .NET
MSBuild ILMerge task - MSBuild ILMerge task is a NuGet package allows you to use the famous ILMerge utility in automated builds and/or Visual Studio projects.
ReactJS.NET - ReactJS.NET is a library that makes it easier to use Babel along with Facebook's React and JSX from C#.
Aeron.NET - Efficient reliable UDP unicast, UDP multicast, and IPC message transport - .NET port of Aeron
TypeShape - TypeShape is a small, extensible F# library for practical generic programming
Streams - A lightweight F#/C# library for efficient functional-style pipelines on streams of data.
Warden - Define "health checks" for your applications, resources and infrastructure. Keep your Warden on the watch
ByteSize - ByteSize is a utility class that makes byte size representation in code easier by removing ambiguity of the value being represented. ByteSize is to bytes what System.TimeSpan is to time.
Jot - a library for persisting and restoring application state (a better alternative to .settings files).
Enums.NET - Enums.NET is a high-performance type-safe .NET enum utility library
HidLibrary - This library enables you to enumerate and communicate with Hid compatible USB devices in .NET.
SystemWrapper - SystemWrapper is .NET library for easier testing of system APIs.
YoutubeExplode - Ultimate library for extracting metadata and downloading Youtube videos and playlists.
DeviceId - Generate a 'device ID' that can be used to uniquely identify a computer.
DeviceDetector.NET - The Universal Device Detection library will parse any User Agent and detect the browser, operating system, device used (desktop, tablet, mobile, tv, cars, console, etc.), brand and model.
NaturalSort.Extension - Extension method for StringComparer that adds support for natural sorting (e.g. "abc1", "abc2", "abc10" instead of "abc1", "abc10", "abc2").
Coravel Near-zero config .NET Core library that makes Task Scheduling, Caching, Queuing, Mailing, Event Broadcasting (and more) a breeze!
Quickenshtein - An extremely quick and memory efficient Levenshtein Distance calculator with SIMD and Threading support
Infinity Crawler - A simple but powerful web crawler library for .NET
Build Versioning - Simple build versioning for .NET, powered by Git tags
SystemTextJson.JsonDiffPatch - High-performance, low-allocating JSON object diff and patch extension for System.Text.Json. Support generating patch document in RFC 6902 JSON Patch format.

MVVM

Community Toolkit - Collection of control & helper libraries and samples for various .NET technologies. Contains modern MVVM library, supported by Microsoft. Includes Windows Community Toolkit, MAUI Community Toolkit, and Dotnet Community Toolkit.
Caliburn.Micro - A small, yet powerful framework, designed for building applications across all XAML platforms. Its strong support for MV* patterns will enable you to build your solution quickly, without the need to sacrifice code quality or testability.
MVVM Light Toolkit - The main purpose of the toolkit is to accelerate the creation and development of MVVM applications in WPF, Silverlight, Windows Store (RT) and for Windows Phone
Catel - Catel is an application development platform with the focus on MVVM (WPF, Silverlight, Windows Phone and WinRT) and MVC (ASP.NET MVC). The core of Catel contains an IoC container, models, validation, memento, message mediator, argument checking, etc.
UpdateControls - Update Controls does not require that you implement INotifyPropertyChanged or declare a DependencyProperty. It connects controls directly to CLR properties. This makes it perfect for the Model/View/ViewModel pattern.
ReactiveUI - An MVVM framework for .NET that integrates the Reactive Extensions (Rx) framework, enabling developers to build elegant, testable applications using WPF, Windows Store Apps, WP8 or Xamarin.
Okra App Framework - An app centric MVVM framework for Windows 8.1 built with dependency injection in mind, including a full set of Visual Studio MVVM templates.
Prism - A cross-platform desktop and mobile MVVM development framework.
Win Application Framework (WAF) - A lightweight Framework that helps you to create well structured WPF and UWP Applications. It supports you in applying a Layered Architecture and the Model-View-ViewModel pattern.
MVVMCross - Cross-platform mvvm mobile development framework for WPF, Silverlight for WP7 and WP8, Mono for Android, MonoTouch for iOS, Windows Universal projects (WPA8.1 and Windows 8.1 Store apps). Makes extensive use of Portable Class Libraries (PCL) to provide maintainable cross platform C# native applications.
Stylet - Minimal MVVM framework inspired by Caliburn Micro, with good documentation, high test coverage, and its own IoC container
Gemini - IDE framework similar in concept to the Visual Studio Shell. Built on WPF, AvalonDock, and Caliburn Micro.
Toms Toolbox - Visual Composition framework to easily build modularized MVVM applications based on the Managed Extensibility Framework (MEF).
MVVM Dialogs - Framework simplifying the concept of opening dialogs from a view model when using MVVM in WPF or UWP.
Smaragd - A platform-independent, lightweight library for developing .NET applications using the MVVM architecture.
EBind - A concise, fast and feature-rich .NET data binding solution.

Networking

NetCoreServer - Ultra fast and low latency asynchronous socket server & client C# .NET Core library with support TCP, SSL, UDP, HTTP, HTTPS, WebSocket protocols and 10K connections problem solution (NETStandard).
SharpPcap - Fully managed, cross platform (Windows, Mac, Linux) .NET library for capturing packets from live and file based devices.

Object to object mapping

AutoMapper - A convention-based object-object mapper in .NET. https://automapper.org
TinyMapper - A tiny and quick object mapper for .NET.
ExpressMapper - A lightweight, lighting fast .NET mapper to map one type of object(s) to another in automated and easy way. ExpressMapper relies completely on the expression trees.
AgileMapper - A zero-configuration Object-Object mapper supporting .NET Standard 1.0
Mapperly - A .NET source generator for generating object mappings. No runtime reflection.
Mapster - A high performance object mapper in .net

Office

ExcelDna - ExcelDna makes it easier to create and deploy Excel Add-Ins using C#, F# or VB .NET
ClosedXML - ClosedXML makes it easier for developers to create Excel 2007/2010 files
NPOI - This project is the .NET version of POI Java project at https://poi.apache.org/.
EPPlus - EPPlus is a .NET library that reads and writes Excel 2007/2010 files using the Open Office XML format (xlsx).
Open XML SDK - The Open XML SDK provides open-source libraries for working with Open XML Documents (DOCX, XLSX, and PPTX).
DocX - DocX is a .NET library that allows developers to manipulate Word 2007/2010/2013 files, it does not require Microsoft Word or Office to be installed.
ExcelDataReader - Lightweight and fast library written in C# for reading Microsoft Excel files (2.0-2007).
NetOffice - .NET wrapper assemblies for Microsoft Office applications.
GemBox.Bundle - A package of .NET components that enable fast, simple and efficient processing of office files (Excel, Word, PowerPoint, PDF and emails). [$]****[Free Lite versions]
Outlook Redemption - Library to work with the Outlook Object Model and (Extended) MAPI. Supports Outlook 98 - 2019. Work with objects/mails/accounts/folders in Exchange and Outlook. [$]
ShapeCrawler - A fluent API for the processing of PowerPoint presentations without Microsoft Office installed.
MiniExcel - A micro Excel helper avoids OOM and high performance to create/mapping/template-fill-data.
Toxy - .NET text extraction framework supports a few file formats

OpenAI

Cledev.OpenAI - .NET SDK for OpenAI which includes ChatGPT, DALL-E and Whisper APIs and a Blazor Server playground.

ORM

Entity Framework 6 - Object-relational mapper that enables .NET developers to work with relational data using domain-specific objects
Entity Framework Core - Object-relational mapper that enables .NET developers to work with relational data using domain-specific objects
EntityFramework.Exceptions - Use typed Exceptions for Entity Framework Core when your SQL query violates database constraints in SqlServer, MySql, PostgreSQL or SQLite
EFCore.BulkExtensions - Entity Framework Core Bulk Extensions for super fast (BulkCopy) CRUD ops + SaveChanges on multiple DBs: SQL, PG, My, Lite.
Dapper - A simple object mapper for .NET by StackExchange
Dapper Extensions - Small library that complements Dapper by adding basic CRUD operations (Get, Insert, Update, Delete) for your POCOs
Dapper.FastCRUD - The fastest micro-ORM extension for Dapper
SqlSugar - Another ORM library supports many RDBMS including MySql, SqlServer, Sqlite, Oracle, Postgresql
FreeSql - a convenient ORM in dotnet, supports MySql, SqlServer, PostgreSQL, Oracle, Sqlite, Firebird, 达梦, 人大金仓, 神舟通用, 翰高 and Access.
NHibernate - NHibernate Object Relational Mapper
Fluent NHibernate - Fluent, XML-less, compile safe, automated, convention-based mappings for NHibernate.
FluentMigrator - Fluent Migrations framework for .net
ServiceStack.OrmLite - Light, simple and fast convention-based POCO ORM [Free for OSS] [$]
Massive - A small, happy, data access tool that will love you forever.
LINQ to DB - The fastest LINQ database access library offering a simple, light, fast, and type-safe layer between your POCO objects and your database.
MicroLite ORM MicroLite ORM is a micro Object Relational Mapper for the .NET framework. It is designed to be easy to use, extensible and testable.
PetaPoco - A tiny ORM-ish thing for your POCOs
AsyncPoco - A long-"awaited" fully asynchronous PetaPoco fork
NPoco - Simple microORM that maps the results of a query onto a POCO object. Based on Schotime's branch of PetaPoco
Limebean - Hybrid ORM which uses SQL fragments and doesn't require Model Classes.
LLBLGen Pro - Entity Modeling solution for Entity Framework, NHibernate, Linq to SQL and its own ORM framework: LLBLGen Pro Runtime Framework. [$][Free Lite version]
Insight.Database - Insight.Database is a fast, lightweight, micro-ORM for .NET
DbExtensions - Data-access framework with a strong focus on query composition, granularity and code aesthetics.
SmartSql - SmartSql = MyBatis + Cache（Memory | Redis）+ ZooKeeper + R / W Splitting + Dynamic Repository ....
RepoDb - A hybrid ORM library for .NET.
Venflow - A super fast and lightweight ORM for PostgreSQL.
MongoFramework - An "Entity Framework"-like interface for MongoDB

Package Management

NuGet - The .NET package manager
BaGet - A cross-platform, lightweight NuGet and Symbol server
Cloudsmith - A fully managed package management SaaS, with support for NuGet, Npm, Docker and much more. [Free for Public/OSS] [$]
MyGet - Hosted Package Repository for NuGet, NPM, Bower and VSIX. Also provides CI as-a-Service. [$]
Paket - A package dependency manager for .NET with support for NuGet packages and GitHub repositories. https://fsprojects.github.io/Paket/
Sleet - A NuGet v3 static feed generator with support for AWS S3 and Azure Storage

PDF

Cloudmersive PDF - Cloudmersive PDF is a native .NET Framework and .NET Core NuGet library and API service that can create, modify, encrypt or convert PDF documents at high scale and fidelity; and is free to use with no expiration [Free]
Docotic.Pdf - PDF library to create, read, edit, draw, and print PDF documents in .NET and .NET Core applications. 100% managed, without unsafe blocks. [$] [Free for OSS]
ITextSharp - iText is a PDF library that allows you to CREATE, ADAPT, INSPECT and MAINTAIN documents in the Portable Document Format (PDF)[$] [Free for OSS]
PdfiumViewer - PdfiumViewer is a PDF viewer based on the PDFium project.
WkhtmlToPdf - C# wrapper around wkhtmltopdf console utility. Allow to generate preety PDF using HTML and CSS.
Pdfium.Net SDK - Advanced C# PDF library for render, create, edit, merge, split, print, and view PDFs. Open source PDF Viewer is available on GitHub. A NuGet package is also available for easy inclusion into your projects.[$]
PdfPig - Read and create and extract text and other content from PDFs in C# (port of PdfBox)
QuestPDF - QuestPDF is an open-source, modern and battle-tested library that can help you with generating PDF documents by offering friendly, discoverable and predictable C# fluent API.
Kevsoft.PDFtk - A wrapper to drive the awesome pdftk binary, which can fill PDF forms, get field information, concatenate multiple documents or pages, split documents, add or replace stamps, and can attach files to or download files from pages.

Profiler

MiniProfiler - A simple but effective mini-profiler for ASP.NET websites
Glimpse - The open source diagnostics platform for the web
Unchase.FluentPerformanceMeter - An open-source and cross-platform .Net Standard 2.0 library that is designed for the method’s performance measurement.

Protocols

SSH.NET - A Secure Shell (SSH) library for .NET, optimized for parallelism. Provides SSH commands, SFTP/SCP uploads and downloads, and SOCKS4/SOCKS5/HTTP proxies.
FluentFTP - An FTP and FTPS library for .NET, optimized for speed. Provides extensive FTP commands, file uploads/downloads and FTP proxies.
SharpSnmpLib - An open source SNMP implementation for .NET/Mono/Xamarin. Versioin 1, 2c, and 3 are supported.
DNS - A library for parsing and serializing DNS messages. Includes a basic DNS client and server.
DnsClient.NET - A simple yet very powerful and high performant open source library for the .NET Framework to do DNS lookups.
Tecan SiLA2 SDK - A library and code generator to develop SiLA2 clients and servers.

Push Notifications

PushSharp - A server-side library for sending Push Notifications to iOS, OSX, Android, Chrome, Windows Phone, Windows 8, Blackberry, and Amazon devices.

Query Builders

SqlKata - Elegant SQL query builder, that supports complex queries, joins, sub queries, nested where conditions, vendor engine targets and more

Queue

CAP - An EventBus with local persistent message functionality for RabbitMQ or Kafka.
NServiceBus - The most popular service bus for .NET
Gofer.NET - Easy C# API for Distributed Background Tasks/Jobs for .NET Core. Inspired by celery for python.
Hangfire - Incredibly easy way to perform fire-and-forget, delayed and recurring tasks inside ASP.NET applications
RabbitMQ.NET - Implementation of an AMQP client library for C#, and a binding exposing AMQP services via WCF
NetMQ - NetMQ is 100% native C# port of ZeroMQ
MassTransit - MassTransit is lean service bus implementation for building loosely coupled applications using the .NET Framework.
Rebus - Rebus is a lean service bus implementation for .NET, similar in nature to NServiceBus and MassTransit, only leaner
RestBus - A service-oriented .NET messaging library for RabbitMQ.
RawRabbit - A modern .NET Core library for RabbitMQ.
EasyNetQ - An easy to use .NET API for RabbitMQ
Warewolf ESB - An easy to use service bus and microservices platform. Easily build applications and services in a visual IDE.
Confluent's .NET Client - Confluent's .NET Client for Apache Kafka.
Foundatio - A common interface with in-memory, Redis and Azure implementations.
Kafunk - F# Kafka client from Jet
Brighter - Command Dispatcher, Processor, and Distributed Task Queue https://www.goparamore.io/
Silverback - A simple but feature-rich message bus for .NET core (supports Kafka, RabbitMQ and MQTT).
SlimMessageBus - Lightweight message bus with transports for popular messaging systems (Kafka, Redis, Azure Service Bus, and others) and in-memory communication.

RPC

gRPC An RPC library and framework for .NET Core. Read more about it on Docs Microsoft
CoreRPC - Extensible library for WCF-like RPC targeting netstandard1.3. Compatible with .NET, Mono and .NET Core.
BloomRPC - BloomRPC aims to provide the simplest and most efficient developer experience for exploring and querying your GRPC services.
gRPCurl - gRPCurl is a command-line tool that lets you interact with gRPC servers. It's basically curl for gRPC servers.
gRPC UI - gRPC UI is a command-line tool that lets you interact with gRPC servers via a browser. It's sort of like Postman, but for gRPC APIs instead of REST.

Reactive Programming

Rx.NET - The Reactive Extensions (Rx) is a library for composing asynchronous and event-based programs using observable sequences and LINQ-style query operators
Dynamic Data - Reactive Extensions (Rx) for collections
ObsevableComputations - A cross-platform .NET library for computations whose arguments and results are objects that implement INotifyPropertyChanged and INotifyCollectionChanged (ObservableCollection) interfaces.

Real-time Communications

SIPSorcery - A cross platform C# .NET library supporting SIP, VoIP and WebRTC.

Regular Expression

RegExtract - Clean & simple idiomatic C# RegEx-based line parser that emits strongly typed results.

Scheduling

FluentScheduler - Task scheduler with fluent interface that runs automated jobs from your application
NCrontab - Class library for parsing & formatting crontab expressions as well as calculating occurrences of time based on a crontab schedule
NCrontab.Scheduler - Simple task scheduler library for scheduling NCrontab-based tasks
QuartzNet - Quartz Enterprise Scheduler .NET
Hangfire - An easy way to perform fire-and-forget, delayed and recurring tasks inside .NET apps
Chroniton - A simple, fully integrable, and customizable library for running strongly typed jobs (tasks) on schedules.
DurableTask - This framework allows users to write long running persistent workflows in C# using the async/await capabilities.
Workflow Core - Lightweight embeddable workflow engine

SDK and API Clients

AWS SDK - The AWS SDK for .NET enables .NET developers to easily work with Amazon Web Services
Azure PowerShell - A set of PowerShell cmdlets for developers and administrators to develop, deploy and manage Microsoft Azure applications
Countly SDK for Windows - Windows SDK for Countly analytics and marketing platform for product and marketing managers
Octokit.NET - A GitHub API client library for .NET
Dropbox.NET - Official .NET SDK for the Dropbox API
Getty Images API SDK - SDK for the Getty Images and iStock APIs
Cloudmersive APIs - An API client library for .NET [Proprietary][Free]

Search

Elasticsearch .NET - Elasticsearch.Net & NEST
PlainElastic.Net - Plain .NET client for ElasticSearch
SolrNet - Solr client for .NET
SolrExpress - A simple and lightweight query .NET library for Solr, in a controlled, buildable and fail fast way
Lucene.net - Lucene.Net is a port of the Lucene search engine library, written in C# and targeted at .NET runtime users

Serialization

Ceras - Ceras is a binary serializer. It converts any object into a byte[] and back. It goes above and beyond in terms of features, speed, and comfort. Supports reference loops, large/complicated inheritance chains, splitting objects into parts and more.
CsvExport - Very simple & lightweight CSV exporter, Excel friendly, escapes text & quotes etc.
Protobuf.NET - Protocol buffers is the name of the binary serialization format used by Google for much of their data communications
Json.NET - Popular high-performance JSON framework for .NET
ServiceStack.Text - JSON, JSV and CSV Text Serializers used in servicestack.net
Msgpack-Cli - MessagePack implementation for Common Language Infrastructure
Jil - Fast .NET JSON serializer, built on Sigil (used by StackOverflow)
ProtoBuf - Generate C# code for protocol buffer serialization from a .proto specification.
FlatSharp - Fast, idiomatic FlatBuffers implementation. Use .fbs files or attributes.
F# Data - F# type providers for accessing XML, JSON, CSV and HTML files (based on sample documents) and for accessing WorldBank data
Bond - cross-platform framework for working with schematized data. It supports cross-language de/serialization and powerful generic mechanisms for efficiently manipulating data.
Hyperion - A high performance polymorphic serializer for the .NET framework.
FileHelpers - free and easy to use .NET library to import or export data from fixed length or delimited records in files, strings or streams.
FsPickler - A fast multi-format message serializer for .NET
Migrant - Fast and flexible serialization framework usable on undecorated classes.
Utf8Json - Fast and Zero Allocation JSON Serializer for C#(.NET, .NET Core, Unity and Xamarin), this serializer write/read directly to UTF8 binary so boostup performance.
ObjectDumper.NET - Serializes in-memory object to C# code.
FluentSerializer - A profile-based Serializer for multiple data-formats.

SMS and Phone calls

Twilio-csharp - A C#/.NET Library for sending and receiving phone calls and text messages with Twilio.

State machines

Stateless - Create state machines and lightweight state machine-based workflows directly in .NET code
Automatonymous - A state machine library for .NET - allows you to write fluent style state machines
LiquidState - Efficient asynchronous and synchronous state machines for .NET

Static Site Generators

FsBlog - Blog aware, static site generation using F#
Pretzel - A site generation tool (and then some) for .NET platforms
Sandra.Snow - Jekyll-inspired static site generation for .NET
Wyam - A simple to use, highly modular, and extremely configurable static content generator

Strong Naming

Strong Namer - Automatically add strong names to referenced assemblies which do not already have a strong name. This will allow you to reference and use (NuGet packages with) assemblies which are not strong named from your projects that do use a strong name.
.NET Assembly Strong-Name Signer - Utility software to strong-name sign .NET assemblies, including assemblies you do not have the source code for.

Style Guide

C# Style Guide - StackOverflow Q & A on style guides
C# Coding Conventions - Official MSDN C# code conventions
C# Async Guidance - list of problematic asynchronous patterns for .NET Core with an explanation of how to solve those issues

Template Engine

RazorEngine - Open source templating engine based on Microsoft's Razor parsing engine
RazorLight - Open source template engine based on Microsoft's Razor parsing engine supporting .NET Standard 2.0
Nustache - Open source library for logic-less templates
Stubble - Trimmed down {{mustache}} templates in .NET. Successor of Nustache.
DotLiquid - C# port of the Ruby Liquid templating language
Mustache Sharp - An extension of the mustache text template engine for .NET.
Scriban - A fast, powerful, safe and lightweight text templating language and engine for .NET
Morestachio - A full sized {{mustache}} like template engine with focus on extendibility.
Fluid - Fluid is an open-source .NET template engine based on the Liquid template language.
SmartFormat - A lightweight text templating library written in C# which can be a drop-in replacement for string.Format
Handlebars.Net - A real .NET Handlebars engine

Testing

ArchUnitNET - Simple library for checking the architecture of C# code with a fluent API.
NetArchTest - A fluent API for .Net Standard that can enforce architectural rules in unit tests.
AutoFixture - AutoFixture is an open source framework for .NET designed to minimize the 'Arrange' phase of your unit tests
BDTest - A behaviour driven testing and reporting framework!
BDDfy - BDDfy is the simplest BDD framework EVER!
Bogus - A simple and sane fake data generator for C#. Based on and ported from the famed faker.js.
ExpressionToCode - Use plain C# syntax in assertions that include both the expression expression and subexpression values in the failure message.
FakeItEasy - The easy mocking library for .NET https://fakeiteasy.github.io
Fluent Assertions - A set of .NET extension methods that allow you to more naturally specify the expected outcome of a TDD or BDD-style test
FluentAutomation - Simple Fluent API for UI Automation
FsCheck - Random Testing for .NET.
Fuchu - A unit-testing library for F# with tests-as-values which makes DSLs extremely easy to create.
Machine.Specifications - Machine.Specifications (MSpec) is a context/specification framework that removes language noise and simplifies tests.
Moq - The most popular and friendly mocking framework for .NET
Moq.Contrib.HttpClient - A set of extension methods for mocking HttpClient and IHttpClientFactory with Moq.
NBomber - Very simple load testing framework for Pull and Push scenarios. It's 100% written in F# and targeting .NET Core and full .NET Framework.
NBuilder - Rapid generation of test objects
NCrunch - An automated continuous & concurrent testing tool for Visual Studio. [$]
NFluent - NFluent is an assertion library which aims to fluent your .NET TDD experience.
NSubstitute - A friendly substitute for .NET mocking frameworks
NUnit - A unit-testing framework for all .NET languages
Rhino Mocks - Dynamic Mocking Framework for .NET
Testcontainers - A library to support tests with throwaway instances of Docker containers for all compatible .NET Standard versions.
SecTester - SecTester is a new tool that integrates Bright enterprise-grade scan engine directly into your integration or e2e tests. [Proprietary] [Free]
Shouldly - Shouldly is an assertion framework which focuses on giving great error messages when the assertion fails while being simple and terse.
Snapshooter - A snapshot testing tool for .NET Core and .NET Framework
SpecFlow - Binding business requirements to .Net code
Stryker.NET - Mutation testing for .NET Core projects
xBehave.net - An xUnit.net extension for describing your tests using natural language.
xUnit.net - A free, open source, community-focused unit testing tool for the .NET Framework.
Canopy - Canopy is a free, open source F# web automation and testing framework
Expecto - A smooth testing framework for F# with tests as values. Unit testing, property based testing, performance testing and stress testing.
ReportPortal - AI-powered Test Automation Dashboard. Acquire, aggregate and analyze test reports to ascertain release health.
Compare-Net-Objects - Perform a deep compare of any two .NET objects using reflection. Shows the differences between the two objects.
Verify - Verification tool to enable simple approval of complex models and documents.
CsCheck - Random testing library for C#. Including concurrency, causal profiling, regression and performance testing.

Tools

Downloader - Fast and reliable multipart downloader with asynchronous progress events for .NET applications.
Fiddler - The free web debugging proxy for any browser, system or platform
Open Live Writer - Blog writer which integrated with WordPress, Blogger, et. al. Open Live Writer makes it easy to write, preview, and post to your blog.
CodeHub - CodeHub is the best way to browse and maintain your GitHub repositories on any iOS device!
ShareX - ShareX is a free and open source program that lets you capture or record any area of your screen and share it with a single press of a key. It also allows uploading images, text or other types of files to over 80 supported destinations you can choose from.
Myrtille - A native HTML4/5 Remote Desktop Protocol client, HTTP gateway written in C# for .NET
Opserver - Stack Exchange's Monitoring System
CatLight - Build status notifications for TFS/Jenkins/Travis/Appveyor. Cross-platform desktop app based on .NET Core and Electron. [Free][Proprietary]
Mockaco - API mock server with fast setup, useful to simulate HTTP responses, leveraging ASP.NET Core features, built-in fake data generation and C# scripting engine powered by Roslyn scripting API.
Netling - A load tester client for easy web testing. It is extremely fast while using little CPU or memory.
Papercut - Papercut is an open source (.NET based) test email viewer that runs locally with a built-in SMTP server designed to receive and notify of test email messages.
Visual Studio Uninstaller - Uninstall and clean up all components of Visual Studio.
Fake JSON Server - Fake REST API for prototyping or as a CRUD Back End. No need to define types, uses dynamic typing. Data is stored to a single JSON file. Has authentication, WebSocket notifications, async long running operations, random generation for errors/delays and experimental GraphQL support.
posh-dotnet - PowerShell tab completion for the dotnet CLI
SmartCode - SmartCode = IDataSource -> IBuildTask -> IOutput => Build Everything!!! (Including [Code generator])
NETworkManager - A powerful tool for managing networks and troubleshoot network problems!
AnyStatus - A desktop notifications app for monitoring CI/CD pipelines, servers, network, health and metrics. AnyStatus supports Azure DevOps, Jenkins, TeamCity, AppVeyor and more.
OctoLinker - Navigate through project.json, packages.config, *.props, *.targets, and C#/F#/VB.NET project files efficiently with the OctoLinker browser extension for GitHub.
YARP - YARP is a reverse proxy toolkit for building fast proxy servers in .NET using the infrastructure from ASP.NET and .NET.
JSON Formatter and Validator - A blazing fast JSON formatter and validator that won't share JSON with a server.
CSharpier - An opinionated code formatter for c# that is based on the Prettier printing process.
UnitsNet - Makes life working with units of measurement just a little bit better.
Another Redis Desktop Manager - A faster, better and more stable redis desktop manager [GUI client], compatible with Linux, Windows, Mac. What's more, it won't crash when loading massive keys.

Trading

Lean - Lean Engine is an open-source fully managed C# algorithmic trading engine built for desktop and cloud usage. https://www.quantconnect.com/lean/
StockSharp - Trading and algorithmic trading open source platform (stock markets, forex, bitcoins and options). https://stocksharp.com

UI Automation

Atata - Automated web testing full featured framework based on Selenium WebDriver.
Managed Windows API - Introspect and automate third-party Windows / VC++ applications without needing its source code.
FlaUI - FlaUI is a .NET library which helps with automated UI testing of Windows applications (Win32, WinForms, WPF, Store Apps, ...).
PuppeteerSharp - Puppeteer Sharp is a .NET port of the official Node.JS Puppeteer API.
PuppeteerSharp.Contrib - Contributions to Puppeteer Sharp that provides a convenient way to write readable and robust browser tests.

Visual Studio Plugins

Web Essentials - Web Essentials extends Visual Studio with lots of new features that web developers have been missing for many years
VsVIM - VIM in Visual Studio
Nuget Package Manager - NuGet is the package manager for the Microsoft development platform including .NET
SideWaffle - A collection of Item Templates for Visual Studio 2012/2013/2015 that makes any web developer's life much easier
Resharper - Developer Productivity Tool for Visual Studio [$]
CodeContracts - Source code for the CodeContracts tools for .NET
Git Diff Margin - Displays live Git changes of the currently edited file on Visual Studio margin and scroll bar
Productivity Power Tools - A set of extensions to Visual Studio Professional (and above) which improves developer productivity.
Tabs Studio - Visual Studio tab manager with multiple tab rows, tab coloring and tab grouping. [$]
VSColorOutput - Color highlighting for Build, Find and Debug output windows. Custom match patterns and colors can be added.
CodeLineage - Easy access to a cumulative diff view between file revisions (supports svn, git, mercurial, perforce).
OzCode - OzCode is a Visual Studio Extension which cuts down on debugging time and increases productivity by detecting and isolating bugs, making them easy to fix. [$]
ViEmu - very powerful Vi/vim emulator for Visual Studio supporting all basic and many advanced features of vi/vim. [$]
Roslynator - A collection of 500+ analyzers, refactorings and fixes for C#, powered by Roslyn
Unchase.Odata.Connectedservice - A Visual Studio Connected Service for generating API client code in C# or VB for OData web service.
Unchase.OpenAPI.Connectedservice - A Visual Studio 2017/2019 extension to generate C# (TypeScript) HttpClient (or C# Controllers) code for OpenAPI web service with NSwag.
SonarSource.sonarlint-visualstudio - SonarLint is a free, open source Visual Studio 2017, 2019 and 2022 extension that provides on-the-fly feedback to developers on new bugs and quality issues in C#, VB.NET, C/C++, TypeScript and JavaScript.

Web Browsers

CefSharp - HTML5, CSS3 and JS web browser powered by Chromium, for WinForms and WPF

Web Frameworks

ASP.NET MVC - ASP.NET is a free web framework for building great web sites and applications
Coalesce - Coalesce is a framework for rapid-development of ASP.NET Core web applications.
FubuMVC - A front-controller style MVC framework for .NET
NancyFx - Lightweight, low-ceremony, framework for building HTTP-based services on .NET and Mono
IISNode - Host Node.js applications in IIS
Suave.IO - Framework/library/web server that makes you cry tears of joy after finishing your project ahead-of-time when you look at the beautiful code you've written in F#.
DotVVM - MVVM framework for people who don't like to write JavaScript, with OWIN and ASP.NET Core support and a free extension for Visual Studio 2015 and 2017.
Giraffe - Functional (F#) ASP.NET Core micro framework for building rich web applications

Web Servers

EmbedIO - Web server built on Mono and cross-platform
XSP - Mono's ASP.NET hosting server. This module includes an Apache Module, a FastCGI module that can be hooked to other web servers as well as a standalone server used for testing (similar to Microsoft's Cassini)

WebSocket

Fleck - Fleck is a WebSocket server implementation in C#. Branched from the Nugget project
SignalR - Library for ASP.NET developers that makes it incredibly simple to add real-time web functionality to your applications
SuperSocket - SuperSocket is a light weight extensible socket application framework
Websocket-Sharp - A C# implementation of the WebSocket protocol client and server
WebSocket4NET - WebSocket client for .NET 2.0+, Xamarin, Mono, Silverlight, Windows Phone, & WinRT
Crossertech - Provides a great set of tools for you to build real-time applications on the Microsoft.NET plattform and much more. [$]
WampSharp - A C# implementation of The Web Application Messaging Protocol - a protocol that provides messaging patterns of Remote Procedure Calls and Publish/Subscribe over WebSockets.
NetGain - A high performance WebSocket server library powering Stack Overflow.
Websockets.PCL - WebSockets.PCL is a portable class library, profile 259, C# WebSocket implementation.
Websocket.Client - A multiplatform wrapper over native C# class ClientWebSocket with built-in reconnection and error handling.

Windows Services

TopShelf - An easy service hosting framework for building Windows services using .NET

WPF

Data Grid Extensions - Modular extensions for the WPF DataGrid control, like filtering, additional column events, extended star-size column behavior, and more...
Extended WPF Toolkit™ - A rich collection of controls, components and utilities for creating WPF applications
WPF - WPF is a .NET Core UI framework for building Windows desktop applications.

Parser Library

Sprache - A simple, lightweight library for constructing parsers directly in C# code
Pidgin - A lightweight, fast and flexible parsing library for C#, developed at Stack Overflow
FParsec - A parser combinator library for F#
Superpower - A C# parser construction toolkit with high-quality error reporting
CSLY - A light embedded C# lexer/parser generator.

Source Generator

M31.FluentAPI - Effortlessly generate fluent APIs for your C# classes.
Supernova.Enum.Generators - A C# source generator to create an enumeration class from an enum type. With this package, you can work on enums very, very fast without using reflection.

Other Lists

.NET-libraries-that-make-your-life-easier - Open Source .NET libraries that make your life easier
awesome-LINQ - A curated collection of awesome LINQ libraries, tools, and more.
awesome-analyzers - A curated list of .NET Compiler Platform ("Roslyn") diagnostic analyzers and code fixes.
C# Algorithms, Data Structures - A list of algorithms and data structures implementations.
Awesome .NET Core - A collection of awesome .NET core libraries, tools, frameworks and software
ASP.NET Core Library and Framework Support - A list of what .NET libraries and frameworks are currently supported by ASP.NET Core and .NET Core).
Awesome .NET Performance - A curated list of awesome .NET Performance books, courses, trainings, conference talks, blogs and most inspiring open source contributors.
awesome-ddd - A curated list of Domain-Driven Design (DDD), Command Query Responsibility Segregation (CQRS), Event Sourcing, and Event Storming resources
Awesome Unity - A categorized community-driven collection of high-quality awesome Unity assets, projects, and resources.
Awesome Xamarin - A collection of interesting libraries/tools for Xamarin mobile projects.
Awesome Roslyn - A curated list of awesome Roslyn books, tutorials, open source projects, analyzers, code fixes, and refactorings.
.NET Open Source Developer Projects - This community maintained list showcases .NET open source projects that are useful for any aspect of the development process.
Awesome Microservices .NET Core - A collection of awesome training series, articles, videos, books, courses, sample projects, and tools for Microservices in .NET Core.
dotnet-console-games - Game examples implemented in .NET console applications.

Resources

Discover .NET - Awesome .NET open source and community resources.
NuGet Trends - Check out NuGet packages adoption and what's trending on NuGet.
Weekly C# Digest - Weekly email newsletter with manually curated top 5 links from the .NET community.
ASP.NET Core Developer Roadmap - A complete guide to become a ASP.NET Developer.

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Awesome Dotnet