Framework One version 2.2 is now available for production use! You can download it from the Framework One page on RIAForge. This includes one bug fix over RC2 (interaction between renderData() and trace output).
The main focus of the 2.2 release is improved support for REST APIs, through the addition of renderData() to simplify returning JSON, XML and plain text results to the caller, as well as more sophisticated route handling via "resource packs" which let you define a family of related routes for a given resource type, using a shorthand notation. For more information, see this blog post about the latest FW/1 release and the roadmap.
As noted previously, the master branch is the current stable release (2.2), and the develop branch has become the next release (2.5). 2.5 will be released next month and will be a stepping stone toward some substantial changes coming in 3.0. For more detail, read this blog post explaining the changes coming in 2.5 and 3.0.