Vavoom is a DOOM source port incorporating Doom, Heretic, Hexen, and a little bit of Quake. It runs on DOS, Windows, and Linux and includes many advanced features like OpenGL and Direct3D support, translucency, freelook, jumping, a client/server architecture with in-game joining, a Quake-style console, a powerful language to describe game logic (Vavoom C), and much more.
