List of Open Source Games

• Abuse (1998), Crack dot Com – Game source code was released as public domain along with the shareware-released media files.^[1]
• Adventure (1976), Crowther/Woods – the original text adventure game, source code is public domain.^[2]
• Aleph One is Bungie software's freed Marathon first-person shooter game.
• Armagetron Advanced is a multiplayer, 3D Tron lightcycle racing game.
• Battle for Wesnoth is an open-source strategy game with RPG elements.
• BZFlag is a free multiplayer multiplatform 3D tank battle game.
• Crimson Fields is a tactical war game in the tradition of Battle Isle.
• Crossfire is an open-source MMORPG.
• Darwinbots is an artificial life simulator.
• Enigma is an Oxyd clone.
• Egoboo is an action RPG game and a clone to Nethack and Rogue.
• FlightGear is a multi-platform flight simulator.
• Freeciv is a clone of Civilization II.
• FreeCol is a remake of Colonization.
• FreeDoom is a set of open source graphics files for open source versions of the Doom engine
• FreeOrion is a multiplayer, turn-based strategy computer game, inspired by the Master of Orion series.
• Frets on Fire is a cross-platform game based on Guitar Hero.
• Frozen Bubble is a Puzzle Bobble type game.
• Globulation 2 is a cross-platform RTS.
• GLtron is a light cycle racing game.
• GNU Chess is a chess program. Xboard (a.k.a. Winboard) is an open-source front-end for it.
• GNU Go is a free program that plays the game of Go.
• Gusanos is a clone of Liero.
• HoverRace is an online multiplayer hovercraft racing game that was once shareware.
• Kiki the nano bot, basically a mixture of the games Sokoban and Kula World.
• Several games are included in KDE; for instance:
  • KBounce
  • Kolf
  • KAsteroids
  • Konquest is a galactic conquest strategy game.
  
  
• Lincity (and its successor LinCity-NG) is a city building game like SimCity.
• Liquid War is a realtime competitive game based on directing liquid particles around a complex environment.
• MegaMek is a computer version of the BattleTech miniatures wargame.
• Micropolis is a GPLv3 version of the original SimCity simulation game.
• Moria is an old roguelike RPG.
• NetHack is a roguelike RPG.
• Netrek is a multiplayer hybrid shooter and real time strategy game.
• Neverball is a 3D platform game similar to Super Monkey Ball.
• Nexuiz is a multiplayer first person shooter.
• Oolite is a recreation of the classic Elite, with updated graphics.
• OpenArena is a first-person shooter based on id Tech 3, Quake III Arena's engine.
• OpenCity a city-building game such as SimCity.
• OpenTTD is an open source port of the Chris Sawyer game Transport Tycoon Deluxe
• Pingus is a real-time puzzle game inspired by Lemmings.
• PokerTH is a poker simulator which follows the Texas Hold 'Em rules and betting system. It allows play against human and computer opponents.
• Project: Starfighter is a two-dimensional, non-linear space shooter with an intricate plot.
• Rocks'n'Diamonds is an open-source, cross-platform, arcade game that contains clones of Boulder Dash, Emerald Mine, Supaplex and Sokoban.
• Red Alert: A Path Beyond is a free multiplayer first-person shooter based on the popular Command and Conquer series: Red Alert.
• Sauerbraten is a multiplayer FPS also known as Cube2.
• Scorched 3D is a game based on the classic DOS game Scorched Earth.
• Simutrans Transport Simulator is a simulator that focuses on the transporting of goods, people, mail and power.
• Slash'EM is a branch of NetHack.
• Solarwolf is a 2d action arcade game.
• Sopwith is a side-scrolling shoot-'em-up.
• Spring is a 3D remake of the Total Annihilation RTS game, fully compatible with the original game's units.
• Stendhal is an open-source multiplayer online adventure game (MMORPG) using the Arianne framework.
• StepMania is a simulator of dance games, mainly Dance Dance Revolution.
• SuperTux is a classic 2D jump and run game.
• SuperTuxKart is inspired by Mario Kart.
• Teeworlds is an multiplayer Worms 2-like shooter.
• TEG (Tacticas Estategicas de Guerra) is an open-source Risk-like game.
• Thousand Parsec is a project with the goal of creating a framework for turn-based space empire building games.
• Tile World is a clone of Chip's Challenge made by Brian Raiter.
• Total Annihilation Spring is the modern remake of old famous RTS "Total Annihilation"
• ToME is a roguelike game based on J.R.R. Tolkien's work.
• TripleA is an Axis & Allies based game.
• Tremulous is a free, open source game that blends a team based FPS with elements of an RTS. Players can choose from 2 unique races, aliens and humans.
• Tux Racer is a 3D OpenGL racing game starring the Linux mascot.
• UFO: Alien Invasion is a 3D, turn-based strategy game that pits humans against aliens.
• UltraStar is a SingStar clone.
• Ur-Quan Masters is the classic Star Control 2 game, re-released under the GPL license.
• Unsigned is a Rock Band clone.
• Vega Strike is a 3D space shooter/strategy game which combines trading, bounty hunting and exploration.
• Vulture's Eye & Vulture's Claw are graphical versions of two roguelike games (NetHack and Slash'EM respectively).
• Warzone 2100 is a 3D RTS and a RTT hybrid.
• World of Padman is a 3D shooter
• Wormux is an open source Worms clone.
• Xbattle is a multiplayer real-time military strategy game and simulator.
• Xconq is a generic turn-based strategic game.
• XEvil is a 2D side scroller with an excessive amount of violence.
• X-Moto is a 2D motorbike game.
• XPilot is a multiplayer asteroids-like game.

this list was taken from :
http://en.wikipedia.org/wiki/Alphabetical_list_of_open_source_games