Free agile arena shooter

Game engine for Return to Castle Wolfenstein

Shoot and survive

First-person shooter game

The Free and Fast Arena Shooter

Source port for Build engine games

Fast paced, first person strategy game

dhewm 3 is a Doom 3 GPL source port

Top-down shooter action RPG

Open Source voxel shooter

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

Free fast paced arena shooter

Classic arena first person shooter

FPS aim trainer

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

Game engine for Classic Doom

Leading the way in newschool multiplayer Doom online

First-person shooter with cooperative in-game map editing

a modern QuakeWorld client focused on competitive online play

Epic story-driven FPS running on the Build Engine

A modernization effort of DOOM-3-BFG

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

Open source first person shooter

Open source first person shooter

Tank digging battle game

Modern cross-platform port of the Descent engine

ReC98 source port of the first Seihou Project game

EDuke32 is an awesome, free homebrew game engine

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

A Quake mod based on the retro shooter SPRAWL