Microsoft released the source for Oxite, their blogging engine that's intended to help .NET developers learn ASP.NET MVC. They also released the source for the Mix site, which was built with Oxite.
Microsoft says that developers can build applications with Oxite, since it has a lot of built-in features like trackbacks, pingbacks, and RSS support.
Are you going to use Oxite to learn ASP.NET MVC? Do you think you could do anything useful with it?