Sauerbraten

Sauerbraten (also known as Cube 2 or Sauer, German for “sour roast”) is a cross-platform, Quake-like, first-person shooter computer game that runs on Microsoft Windows, Linux, FreeBSD and Mac OS X using OpenGL and SDL. The game features single-player and multiplayer game play and contains an in-game level editor, its main feature. The game engine is free and open source software, under the Zlib License,[2] with commercial support available from the developer's own business counterpart, Dot3 Labs.[3]

The game started as a redesign to the original Cube Engine, and its first release was made on May 6, 2004. The latest release, dubbed the "CTF Edition", debuted on June 17, 2008.