What platforms support .NET?
Right now the only operating system with a full implementation of .NET (that I know about, anyway) is Microsoft Windows. The .NET Framework redistributable is available for Windows 98, Windows NT, Windows 2000, and Windows XP. The .NET Framework SDK is available for Windows 2000 and Windows XP. The Mono Project is an ongoing open-source implementation of .NET for Linux and Windows that is currently still in development. The dotGNU project is another open-source .NET implementation. The Rotor project is a Microsoft shared source CLI implementation targeting Windows and FreeBSD. Thanks to Brad Wilson for telling me about Rotor, and for reminding me about dotGNU.