A free first person shooter for Mac, PC and Linux

Epic story-driven FPS running on the Build Engine

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

Tank digging battle game

Free agile arena shooter

Free fast paced arena shooter

Fast paced, first person strategy game

The Free and Fast Arena Shooter

Game engine for Return to Castle Wolfenstein

Classic arena first person shooter

a modern QuakeWorld client focused on competitive online play

Leading the way in newschool multiplayer Doom online

Shoot and survive

Source port for Build engine games

Open source first person shooter

A Quake mod based on the retro shooter SPRAWL

First-person shooter with cooperative in-game map editing

Game engine for Classic Doom

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

Top-down shooter action RPG

EDuke32 is an awesome, free homebrew game engine

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

Dhewm 3 is a Doom 3 GPL source port

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

FPS aim trainer

Open Source voxel shooter

Modern cross-platform port of the Descent engine

A modernization effort of DOOM-3-BFG

Open source first person shooter

ReC98 source port of the first Seihou Project game