The only really interesting part of .net to me is the F# language, which is ocaml for .net with sugary monad support. The language itself was recently open sourced, there's a VS vim plugin written in the language, and there's at least some game development going on in the language. F# is my language this year and I'm using it as an excuse to learn the environment. I've always been more impressed with .net and its attendant technologies than I have been with the JVM.
OSS on .net is weird in that commercial pressures and Microsoft's anchoring of the system warp it a bit. Things are located in weird places (codeplex) and discussions happen in weird places. The community is also fairly cut off from the *nix oriented OSS community. I run across stuff randomly that I'm surprised is .net and open source but it's intermittent since I'm mostly in the normal OSS ecosystem and am not particularly well connected to the .net world.
OSS on .net is weird in that commercial pressures and Microsoft's anchoring of the system warp it a bit. Things are located in weird places (codeplex) and discussions happen in weird places. The community is also fairly cut off from the *nix oriented OSS community. I run across stuff randomly that I'm surprised is .net and open source but it's intermittent since I'm mostly in the normal OSS ecosystem and am not particularly well connected to the .net world.