whatsmeow is a Go library for the WhatsApp web multidevice API.
Matrix room: #whatsmeow:maunium.net
For questions about the WhatsApp protocol (like how to send a specific type of message), you can also use the WhatsApp protocol Q&A section on GitHub discussions.
The godoc includes docs for all methods and event types. There's also a simple example at the top.
Also see mdtest for a CLI tool you can easily try out whatsmeow with.
Most core features are already present:
Things that are not yet implemented: