Game engine for Return to Castle Wolfenstein

A Quake mod based on the retro shooter SPRAWL

First-person shooter with cooperative in-game map editing

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

A modernization effort of DOOM-3-BFG

Open source first person shooter

Dhewm 3 is a Doom 3 GPL source port

Epic story-driven FPS running on the Build Engine

The orb ponderer's arena first-person shooter

FPS aim trainer

ReC98 source port of the first Seihou Project game

Tank digging battle game

Open source first person shooter

Top-down shooter action RPG

Fast arcade first person shooter

The Free and Fast Arena Shooter

First-person shooter game

EDuke32 is an awesome, free homebrew game engine

a modern QuakeWorld client focused on competitive online play

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

A free first person shooter for Mac, PC and Linux

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

Modern cross-platform port of the Descent engine

Free fast paced arena shooter

Leading the way in newschool multiplayer Doom online

Classic arena first person shooter

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

Fast paced, first person strategy game

Free agile arena shooter

Open Source voxel shooter