Free fast paced arena shooter

A Quake mod based on the retro shooter SPRAWL

Tank digging battle game

Shoot and survive

A free first person shooter for Mac, PC and Linux

The Free and Fast Arena Shooter

Source port for Build engine games

Open source first person shooter

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

Epic story-driven FPS running on the Build Engine

Dhewm 3 is a Doom 3 GPL source port

a modern QuakeWorld client focused on competitive online play

FPS aim trainer

First-person shooter game

Leading the way in newschool multiplayer Doom online

Open source first person shooter

Game engine for Classic Doom

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

EDuke32 is an awesome, free homebrew game engine

Classic arena first person shooter

Free agile arena shooter

Game engine for Return to Castle Wolfenstein

First-person shooter with cooperative in-game map editing

Open Source voxel shooter

ReC98 source port of the first Seihou Project game

Top-down shooter action RPG

Fast paced, first person strategy game

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

A modernization effort of DOOM-3-BFG

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