The orb ponderer's arena first-person shooter

Open Source voxel shooter

Free agile arena shooter

Game engine for Return to Castle Wolfenstein

ReC98 source port of the first Seihou Project game

Open source first person shooter

Shoot and survive

Epic story-driven FPS running on the Build Engine

A Quake mod based on the retro shooter SPRAWL

Free fast paced arena shooter

Dhewm 3 is a Doom 3 GPL source port

Leading the way in newschool multiplayer Doom online

Game engine for Classic Doom

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

FPS aim trainer

Source port for Build engine games

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

A modernization effort of DOOM-3-BFG

Open source first person shooter

Fast paced, first person strategy game

a modern QuakeWorld client focused on competitive online play

The Free and Fast Arena Shooter

EDuke32 is an awesome, free homebrew game engine

Classic arena first person shooter

Top-down shooter action RPG

Modern cross-platform port of the Descent engine

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

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

Tank digging battle game

First-person shooter with cooperative in-game map editing