Open source first person shooter

Game engine for Classic Doom

Free agile arena shooter

First-person shooter game

FPS aim trainer

The Free and Fast Arena Shooter

Aliens vs Humans, First Person Shooter game with elements of Real Time Strategy

Fast paced, first person strategy game

Fast arcade first person shooter

Open Source voxel shooter

Open Source voxel shooter

Yamagi Quake II is an alternative client for id Software's Quake II

a modern QuakeWorld client focused on competitive online play

Shoot and survive

Open source first person shooter

EDuke32 is an awesome, free homebrew game engine

Free fast paced arena shooter

Classic arena first person shooter

A Zandronum 3.0 fork with improved netcode, configurable movement and many small tweaks

The orb ponderer's arena first-person shooter

First-person shooter with cooperative in-game map editing

A modernization effort of DOOM-3-BFG

Top-down shooter action RPG

Tank digging battle game

ReC98 source port of the first Seihou Project game

Source port for Build engine games

Modern cross-platform port of the Descent engine

Dhewm 3 is a Doom 3 GPL source port

Leading the way in newschool multiplayer Doom online

Epic story-driven FPS running on the Build Engine