Free agile arena shooter

Modern cross-platform port of the Descent engine

First-person shooter game

Epic story-driven FPS running on the Build Engine

A Quake mod based on the retro shooter SPRAWL

Fast paced, first person strategy game

Open source first person shooter

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

Open source first person shooter

Top-down shooter action RPG

The Free and Fast Arena Shooter

Leading the way in newschool multiplayer Doom online

Source port for Build engine games

Classic arena first person shooter

Open Source voxel shooter

a modern QuakeWorld client focused on competitive online play

Tank digging battle game

Shoot and survive

Free fast paced arena shooter

First-person shooter with cooperative in-game map editing

A modernization effort of DOOM-3-BFG

FPS aim trainer

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

Game engine for Classic Doom

dhewm 3 is a Doom 3 GPL source port

EDuke32 is an awesome, free homebrew game engine

Game engine for Return to Castle Wolfenstein

A modern cross‑platform port of “STAR WARS™: Dark Forces” with mod support

The orb ponderer's arena first-person shooter

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