People often think of open source as being purely a Linux and BSD thing. Perhaps they're aware of open source on OS X as well, but in general Windows is seen as hostile to open source. And at the heart of the hostility surely must be Microsoft's proprietary .NET framework, right? But no: the
Mono Project provides a cross-platform, open source implementation of .NET. Version 2.0 was
released this week, and it has matured into a serious development framework.