The RAP Developer's Guide is the official documentation for RAP. It also contains the complete API reference. You can always browse the latest version online. The developer's guide is also available in the Eclipse IDE for offline use if you installed the RAP Tools.
If you are migrating a RAP 2.x (or 1.x) application to RAP 3.x, take a look at the RAP 3.0 Migration Guide. This document lists all breaking changes in RAP 3.0 and explains the necessary steps.
For every new RAP version, we summarize all new features and noteworthy changes on a separate “New and Noteworthy” page.
The RAP Wiki provides more in-depth technical and organizational information. It contains a list of Frequently Asked Questions (FAQ), a list of known add-ons, guides for integrating RAP with other projects, articles on RAP internals, and resources for committers.
As a RAP developer, you should be familiar with a number of base technologies. We've collected a couple of resources that we recommend to read: