Sauerbraten (a.k.a. Cube 2) is a free, open source, both multi & singleplayer first person shooter game. It was built as a major redesign of it's predecessor the Cube by Lee Salzman, Wouter van Oortmerssen (the original creator), Mike Dysart & Robert Pointon. Just like in the original game, the main emphasis falls not on the pretty graphics & load of functions, but on seamless and dynamic in-game map/geometry editing. In the latest version of Sauerbraten gamers playing together online can even co-edit a level at the same time.