Free agile arena shooter

ReC98 source port of the first Seihou Project game

Classic arena first person shooter

Open source first person shooter

Shoot and survive

Epic story-driven FPS running on the Build Engine

Open Source voxel shooter

The Free and Fast Arena Shooter

Modern cross-platform port of the Descent engine

A Quake mod based on the retro shooter SPRAWL

Leading the way in newschool multiplayer Doom online

The orb ponderer's arena first-person shooter

EDuke32 is an awesome, free homebrew game engine

First-person shooter game

A modernization effort of DOOM-3-BFG

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

Top-down shooter action RPG

FPS aim trainer

Game engine for Return to Castle Wolfenstein

Source port for Build engine games

a modern QuakeWorld client focused on competitive online play

Game engine for Classic Doom

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

Free fast paced arena shooter

Dhewm 3 is a Doom 3 GPL source port

Fast paced, first person strategy game

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

First-person shooter with cooperative in-game map editing

Open source first person shooter

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