Open source first person shooter

Game engine for Classic Doom

Free agile arena shooter

FPS aim trainer

Open Source voxel shooter

Free fast paced arena shooter

Open Source voxel shooter

The Free and Fast Arena Shooter

Fast paced, first person strategy game

EDuke32 is an awesome, free homebrew game engine

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

First-person shooter game

Modern cross-platform port of the Descent engine

Source port for Build engine games

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

Open source first person shooter

First-person shooter with cooperative in-game map editing

Classic arena first person shooter

Fast arcade first person shooter

A modernization effort of DOOM-3-BFG

The orb ponderer's arena first-person shooter

Tank digging battle game

Epic story-driven FPS running on the Build Engine

a modern QuakeWorld client focused on competitive online play

ReC98 source port of the first Seihou Project game

Leading the way in newschool multiplayer Doom online

Game engine for Return to Castle Wolfenstein

Top-down shooter action RPG

Dhewm 3 is a Doom 3 GPL source port

Shoot and survive