Prism Composite Application Guidance for WPF team (Gosh, what a name!) published the first release candidate.
The Composite Application Guidance for WPF is designed to help you more
easily build enterprise-level Windows Presentation Foundation (WPF)
client applications. This guidance will help you design and build
flexible composite WPF client applications – applications that use
loosely coupled, independently evolvable pieces that work together
within the overall application.
The release description states that the final release will be on MSDN within a couple of weeks.