Sauerbraten is a free First-Person Shooter game (open-source under a GPL license). It's fairly easy to install on Windows, Mac OS X, or Linux, though on Windows you need to be sure to execute the .BAT file to start the game, instead of the .EXE, which makes more sense. It's a lot of fun to play Regen Capture (a capture-the-flag type of game mode) on the public servers, and to create your own maps using the easy to operate cube-based level editor.

• Towerland - You'd better watch your back. Otherwise you'll be sniped. Towerland has, as it's name suggests, a large amount of towers, connected by multi-level bridges, jump pads, and tunnels. And the surface of the map is just, well, the surface. Below the ground you'll find a maze of narrow, twisting tunnels, offering plenty of reward for the dangers that lie in wait. In Towerland you had better watch your back at all times, because chances are someone's just waiting to pick you off from a distant tower. [Download]