Mesh Align Plus helps you move things around, precisely: arrange objects in your scene, align mesh parts to each other while you're modeling, and create complex custom transformations using measurements from your models.
In short: You choose from a basic set of operations, pick reference points, and apply custom transformations to a variety of targets. Flexible reference picking and a depth of customization enable sophisticated results.
Some real world examples of things you can do with the addon:
Mesh Align Plus is designed to provide precision modeling capabilities, especially for hard surface modelers, mechanical, architectural and CAD/CAM users. See the simple demo clips below for a general sense of what the addon can do, read the Wiki above (with tons of GIF's), or watch the video tutorial on YouTube.