A free first person shooter for Mac, PC and Linux

Game engine for Classic Doom

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

Open source first person shooter

Free fast paced arena shooter

Source port for Build engine games

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

FPS aim trainer

Shoot and survive

Epic story-driven FPS running on the Build Engine

Open Source voxel shooter

The Free and Fast Arena Shooter

Open Source voxel shooter

The orb ponderer's arena first-person shooter

Tank digging battle game

Free agile arena shooter

a modern QuakeWorld client focused on competitive online play

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

First-person shooter game

Top-down shooter action RPG

ReC98 source port of the first Seihou Project game

Leading the way in newschool multiplayer Doom online

Fast paced, first person strategy game

EDuke32 is an awesome, free homebrew game engine

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

First-person shooter with cooperative in-game map editing

A Quake mod based on the retro shooter SPRAWL

Classic arena first person shooter

Modern cross-platform port of the Descent engine

Open source first person shooter