Fast paced, first person strategy game

Free agile arena shooter

First-person shooter game

Classic arena first person shooter

Leading the way in newschool multiplayer Doom online

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

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

Shoot and survive

Free fast paced arena shooter

The Free and Fast Arena Shooter

Open source first person shooter

ReC98 source port of the first Seihou Project game

The orb ponderer's arena first-person shooter

Open Source voxel shooter

First-person shooter with cooperative in-game map editing

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

Game engine for Return to Castle Wolfenstein

Top-down shooter action RPG

Open source first person shooter

FPS aim trainer

a modern QuakeWorld client focused on competitive online play

A Quake mod based on the retro shooter SPRAWL

Game engine for Classic Doom

Source port for Build engine games

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

Epic story-driven FPS running on the Build Engine

Modern cross-platform port of the Descent engine

Tank digging battle game

A modernization effort of DOOM-3-BFG

EDuke32 is an awesome, free homebrew game engine