Lemans: The Vbulletin project is a forum made from an open source internet programming language. It is stored on an open source database. It is a web based version of UNIX based bulletin boards from long ago. IIRC, it's stored and updated via a CVS (?) system, which is also open source. It is cross compatible with every OS in existance thanks to it's architecture.
If windows didn't exist, Vbulletin still would. It might look different, but it would still work the same way.