Vavoom is Doom/Heretic/Hexen/Strife source port. It features software, OpenGL and Direct3D rendering, VavoomC scripting language, slopes, 3D-floors, Quake style lighting engine, pure client/server architecture with in-game joining and a lots more.
This was an awesome engine when it was maintained; it had great graphics (high-res and 3d models) and an amazing scripting language (VavoomC) which allowed for complete modding of game logic. However, the current version has serious problems in Linux, while the windows version in Wine can leave your screen resolution set stuck in the wrong settigs. Unfortunately, its web page is gone, implying its no longer being maintained.