QuakeSpasm is a *Nix friendly Quake Engine based on the SDL port of the popular FitzQuake. It includes some new features, important fixes, and aims for portability and 64 bit correctness. It is available for Windows, Linux and Mac OS X.
Quote: Changes in 0.85.6
More work for string buffer safety
Reverted v0.85.5 change of not allowing deathmatch and coop cvars to be set at the same time (was reported for possibility of causing compatibility issues with mods)