Cube 2: Sauerbraten is a free multiplayer/singleplayer first person shooter, built as a major redesign of the Cube FPS.
Much like the original Cube, the aim of this game is not necessarily to produce the most features & eyecandy possible, but rather to allow map/geometry editing to be done dynamically in-game, to create fun gameplay and an elegant engine.

This great FPS is available for: Windows, Linux and MacOS X.
The game currently has singleplayer and multiplayer modes. Multiplayer functionality is possible with LAN, Local, and Internet play, which gets its server listings from a master server.

Online offers deathmatch, last man standing, Capture , Quake-style Capture the Flag, also instagib versions of some of the game modes (Instagib, Insta-clan-arena, insta-capture) as well as online cooperative map editing, which is one of Sauerbraten's most interesting and popular features.
There are also single player modes featuring both episodic gameplay and also deathmatch on multiplayer maps with AI bots instead of human opponents over the internet.