The orb ponderer's arena first-person shooter

Open source first person shooter

Fast paced, first person strategy game

Shoot and survive

Tank digging battle game

A modernization effort of DOOM-3-BFG

a modern QuakeWorld client focused on competitive online play

Leading the way in newschool multiplayer Doom online

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

Source port for Build engine games

The Free and Fast Arena Shooter

Open Source voxel shooter

dhewm 3 is a Doom 3 GPL source port

Open source first person shooter

Top-down shooter action RPG

Game engine for Classic Doom

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

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

Epic story-driven FPS running on the Build Engine

Free fast paced arena shooter

Classic arena first person shooter

ReC98 source port of the first Seihou Project game

EDuke32 is an awesome, free homebrew game engine

First-person shooter with cooperative in-game map editing

Free agile arena shooter

FPS aim trainer

A Quake mod based on the retro shooter SPRAWL

Game engine for Return to Castle Wolfenstein

Modern cross-platform port of the Descent engine

First-person shooter game