A free first person shooter for Mac, PC and Linux

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

Open source first person shooter

Game engine for Classic Doom

Source port for Build engine games

Shoot and survive

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

Free fast paced arena shooter

Open Source voxel shooter

Epic story-driven FPS running on the Build Engine

Leading the way in newschool multiplayer Doom online

a modern QuakeWorld client focused on competitive online play

First-person shooter game

The orb ponderer's arena first-person shooter

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

Tank digging battle game

ReC98 source port of the first Seihou Project game

Free agile arena shooter

FPS aim trainer

Top-down shooter action RPG

EDuke32 is an awesome, free homebrew game engine

Open Source voxel shooter

The Free and Fast Arena Shooter

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

First-person shooter with cooperative in-game map editing

Fast paced, first person strategy game

A Quake mod based on the retro shooter SPRAWL

Classic arena first person shooter

Dhewm 3 is a Doom 3 GPL source port

Open source first person shooter