Quake III Arena is a first-person shooter game engine and arena combat simulator. It consists of the original C++ game source code for a cross-platform 3D game designed to run on Windows, Linux, and Mac. The project provides the source code necessary to render a first-person shooter experience, focusing on player-versus-player battles in closed 3D environments. It serves as a resource for legacy game preservation and the study of early 3D game engine construction. The engine incorporates spatial partitioning, client-side prediction, and state synchronization to manage multiplayer networking
Freedoom is an entirely free software game based on the Doom engine.
GZDoom is a feature centric port for all Doom engine games, based on ZDoom, adding an OpenGL renderer and powerful scripting capabilities
