Free open source first person shooter game

I've been following the development of Nexuiz for two years now and I decided today to finally download it and give it a try. Nexuiz is a free open-source first person shooter that runs on Windows, Linux and OSX. It is a fast paced 3D deathmatch game project created online by a team of developers. I've just spent half an hour playing it and I must say that for a game that doesn't cost me anything, it really kicks ass big time. Go download it!