Most...ok, all of the projects I run on CodePlex are "extensible" in the sense that I'll gladly take bug fixes, enhancements, etc. (so long as there's testing, the bug fix is actually a bug, the enhancement is worth it, etc.). Of course, I'm doubting anyone would want to work on the stuff I have up their either! However, I think Spackle.NET is the exception. It's a project that's not a huge framework; it's simply a bunch of small helper classes and extension methods that could be used in most any .NET-based application. If you have something that you'd like to add to the project, please let me know and we'll talk.