This Codeplex site will feature demos, samples, and helper libraries related to the selection and activation of the CLR: http://clractivation.codeplex.com/
With .Net Framework 4 and VS 2010 the new ability to load multiple versions of the runtime has changed the way a version is chosen for any particular piece of managed code and gives developers much more control over the runtime their code will end up running against. For a detailed introduction to this new functionality you can see this MSDN magazine article. This CodePlex project will focus on the various ways to start up the runtime and how to influence these choices using the new runtime activation APIs introduced in .Net Framework 4. Our first two projects include a helper library to ease migration from the old to the new APIs and a managed wrapper of our new native activation APIs.