Syntensity isn’t a single game, but rather a platform that can run all kinds of 3D games. There are already a few games, and anybody can create their own. The main game is a multiplayer first/third person shooter (sort of like Quake 3 Arena), and there is also a simple drawing game (in which multiple people can draw and see what each other are drawing in realtime). You can see both games in action in this video.