Tank digging battle game

Open Source voxel shooter

Game engine for Return to Castle Wolfenstein

ReC98 source port of the first Seihou Project game

A Quake mod based on the retro shooter SPRAWL

The orb ponderer's arena first-person shooter

Top-down shooter action RPG

Epic story-driven FPS running on the Build Engine

Open source first person shooter

Shoot and survive

Free fast paced arena shooter

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

Leading the way in newschool multiplayer Doom online

Modern cross-platform port of the Descent engine

Source port for Build engine games

The Free and Fast Arena Shooter

Free agile arena shooter

Game engine for Classic Doom

A modernization effort of DOOM-3-BFG

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

Dhewm 3 is a Doom 3 GPL source port

FPS aim trainer

EDuke32 is an awesome, free homebrew game engine

First-person shooter game

First-person shooter with cooperative in-game map editing

Classic arena first person shooter

Fast paced, first person strategy game

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

Open source first person shooter

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