A notable open source project has come to my attention today called coLinux. It is similar to Cygwin (a Linux command-line shell on Windows), except that it allows you to run Linux GUI with Windows. Haven’t got around to playing with it, but it looks very interesting.
In other news, the latest version of the PlayFair program is now at 0.5.0. Numerous bug fixes as well as a OS X GUI client and a Windows release are featured. The PlayFair project is also now available at FreshMeat.