I haven't checked this out yet, but the description (found via Digg.com) sounds pretty cool. An open source IDE alternative to VS 2005. Capable of creating .NET 1.0, 1.1, and 2.0 assemblies.
I'm going to be diving into some of the more obscure .NET topics in the next few weeks / months in preparation for the certification tests. Well, at least these are the obscure topics that *I* have not encountered along the way.