FPS
Xonotic - Its a fork of the original Nexuiz, and more or less continues what it started. Featuring weapons with alt fire, high configurability, player statistics, vehicles and turrets, mutators like the grappling hook and the jetpack, lots of modes, grafix, etc http://xonotic.org/
Warsow - Cel shaded arena FPS that is similiar to CPMA (Quake 3 mod), biggest difference is that theres a context sensitive key that makes you either dash, dash up stairs, walljump etc. Has a mode similiar to Counter Strike called bomb. https://www.warsow.gg/
ET Legacy (Wolfenstein Enemy Territory) - Team/objective based FPS set in World War II. Its a fork of Wolfenstein Enemy Territory's source code release, basically the same game with the same assets. https://www.etlegacy.com/
nQuake - Easy to install Quake/Quakeworld, free of charge. Uses shareware/free assets, can use the commercial assets as well if you have them. http://nquake.com/
Classic Fortress (Team Fortress) - Revitalization of the original Team Fortress mod for Quake 1. http://classicfortress.net/
Freedoom - Free IWAD replacements for Doom 1 and 2 if you don't want to/can't buy or pirate. Use with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. https://freedoom.github.io/
BZFlag - Multiplayer tank FPS inspired by Battlezone, the old arcade game. http://bzflag.org/
Reaction Quake 3 - Action Quake inspired multiplayer FPS on the ioquake3 engine. http://www.rq3.com/
OpenArena - Quake 3 Arena with free assets, basically http://www.openarena.ws
AssaultCube - Fun and easy to pick up multiplayer FPS. It can run on a Pentium III http://assault.cubers.net/
AssaultCube Reloaded - Fork of AssaultCube, focus is to improve AssaultCube. http://acr.victorz.ca/
Zero Ballistics - Multiplayer tank FPS with Deathmatch, Team Deathmatch, Soccer and BeaconStrike modes. Roam around blasting eachother with tanks, theres multiple weapons and abilities as well. http://www.zeroballistics.com/
Red Eclipse - Arena FPS that differs from the typical arena FPS formula. It has "parkour" moves, an energy bar for parkour/certain kinds of jumping, and alt fires for most weapons. Its a fork of Cube 2: Sauerbraten, so it has in-game map editing too. http://redeclipse.net/
Cube 2: Sauerbraten - Basic multiplayer FPS with a in-game map editing mode with online cooperative editing as well and some rudimentary singleplayer campaigns. Has probably one of the best instagib modes around. Red Eclipse and Tesseract are forks of it. http://sauerbraten.org/
Unvanquished - Multiplayer FPS/RTS, aliens vs humans. A fork of Tremulous, more or less same idea gameplay wise with graphical improvements on a newer engine, still in alpha though. https://www.unvanquished.net/
Terminal Overload - Experimental multiplayer FPS with Tribes-like movement and Tron visuals. http://www.terminal-overload.org/
Uebergame - Multiplayer modern styled FPS thats in development, has team and regular deathmatch and "paintball" variations of the same two modes. Its alpha quality stuff so don't expect much. It also has what appears to be a fairly advanced ingame level editor. http://duion.com/games/uebergame/main
Aleph One (Marathon series) - Play the Marathon games for free on this engine! https://alephone.lhowon.org/ and also play some community made stuff https://alephone.lhowon.org/scenarios.html
Chex Quest 3 - Its actually all three Chex Quest games. WARNING: ZDoom and GZDoom have proprietary software in them, see http://zdoom.org/wiki/license Take the WAD and/or .pk3 files from this game and use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. http://www.chucktropolis.com/gamers.htm
Action Doom 2 - Stylish first person beat em up/shooter. WARNING: ZDoom and GZDoom have proprietary software in them, see http://zdoom.org/wiki/license Take the WAD and/or .pk3 files from this game and use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. http://action.mancubus.net/index.htm
Harmony - WARNING: ZDoom and GZDoom have proprietary software in them, see http://zdoom.org/wiki/license Take the WAD and/or .pk3 files from this game and use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. http://rabotik.nl/harmony.htm
HacX - WARNING: ZDoom and GZDoom have proprietary software in them, see http://zdoom.org/wiki/license Take the WAD and/or .pk3 files from this game and use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. http://drnostromo.com/hacx/page.php?content=download
Adventure of Square - A fun game in the vein of Chex Quest where you play as a square shooting all sorts of other shapes. WARNING: ZDoom and GZDoom have proprietary software in them, see http://zdoom.org/wiki/license Take the WAD and/or .pk3 files from this game and use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. http://adventuresofsquare.com/
Blasphemer - Free Heretic IWAD replacement. Use with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. https://code.google.com/archive/p/blasphemer/
Mega Man 8-bit Deathmatch - Multiplayer Mega Man FPS. WARNING: ZDoom and GZDoom have proprietary software in them, see http://zdoom.org/wiki/license Take the WAD and/or .pk3 files from this game and use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc. http://cutstuff.net/mm8bdm/
Cytadela - Experience the deadliness of walls in this conversion of an old Amiga FPS. http://cytadela.sourceforge.net/
Nocturne In Yellow - GLOOME engine game made by TerminusEst13, the creator of the Demonsteele mod for Doom http://contest.gamedevfort.com/submission/657#.VtzdbZwrKM8
Excalibur: Morgana's Revenge - Enjoy some good old FPS action as you travel through time from places like the jungles of the Jurassic to the castles of Camelot in this Aleph One engine game. http://emr.excaliburworld.com/emr3/
Smokin' Guns - Multiplayer spaghetti western FPS made with ioquake3. The most interesting mode is the bank robbery mode. http://www.smokin-guns.org/
Cube - The predecessor of Cube 2: Sauerbraten. Hasn't been updated since 2005, but it has a few nice singleplayer maps worth playing, like Revenge. http://cubeengine.com/cube.php
Iceball - Ace of Spades clone, still early in development. http://iceball.build/
OpenSpades - Ace of Spades clone. Client software is open source (what runs on your computer), server software is closed source https://github.com/yvt/openspades/releases/tag/v0.0.11
Doom/Hexen/Heretic/Strife/etc - Requires original game data, which is an IWAD typically. Use it with an open source engine like GLOOME, GZDoom-GPL, Vavoom, Prboom, etc.
Quake: Requires original game data. Faithful fork: http://quakespasm.sourceforge.net/ Graphics focused fork, with less faithfulness: https://icculus.org/twilight/darkplaces/ Online play fork: http://ezquake.sourceforge.net/
Quake 2: Requires original game data. Faithful fork: http://www.yamagi.org/quake2/ Graphics focused fork: http://quake2xp.sourceforge.net/ Online play fork: http://quetoo.org/
Quake 3: Arena: Requires original game data. Pretty much vanilla fork https://ioquake3.org/ ioquake3 fork with four player splitscreen, improved bot AI, modding improvements, etc. http://spearmint.pw/
Doom 64 EX - Requires original game data. https://doom64ex.wordpress.com/
Hexen II - Requires original game data. http://uhexen2.sourceforge.net/
Doom 3: Requires original game data. https://github.com/dhewm/dhewm3 WIP fork: http://www.iodoom3.org/
Doom 3: BFG Edition: Requires original game data. https://github.com/RobertBeckebans/RBDOOM-3-BFG
Rise of the Triad - Requires original game data. https://github.com/videogamepreservation/rott
Serious Sam - Requires original game data. https://github.com/rcgordon/Serious-Engine
RTS/RTT
Zero-K and other Spring engine games - Most are similiar to Total Annihilation http://zero-k.info/ and https://springrts.com/wiki/Games
0 A.D. - 3D Age of Empires essentially. https://play0ad.com/
Warzone 2100 - Post apocalyptic/futuristic RTS, features ability to design your own tanks and lots of teching up. https://wz2100.net/
OpenRA - Clones of Red Alert/Dune 2000/Tiberian dawn with balance changes. http://www.openra.net/
Widelands - Much slower and more involved with economy than most RTSes. Its like Settlers II, but better. https://wl.widelands.org/
OpenClonk - Not a typical RTS game, its a Clonk clone. http://www.openclonk.org/
Colobot: Gold Edition - A mix of RTS and programming in a third person view https://colobot.info/
Seven Kingdoms - https://7kfans.com/
Globulation 2 - RTS game where micromanagement is reduced by way of automatic assignment of tasks to units, also features a scripting language and an integrated map editor. Has potato graphics, I'm not sure what happened to the first Globulation. https://globulation2.org/wiki/Main_Page
Wyrmsun - Similiar to Warcraft II, free on Steam but has paid DLC, apparently the game data is available on github, so you could probably compile the game and use the data. https://andrettin.github.io/
Wargus (Warcraft II) - Requires original game data. https://wargus.github.io/
FreeSynd (Syndicate) - Requires original game data. http://freesynd.sourceforge.net/
Freeserf (The Settlers) - Requires original game data. http://jonls.dk/freeserf/
Return to the Roots (The Settlers II) - Requires original game data. https://www.siedler25.org/
Dune Legacy (Dune 2) - Requires original game data. http://dunelegacy.sourceforge.net/website/
Stargus (Starcraft) - Requires original game data. Currently unfinished, some major features don't work. http://stargus.stratagus.com/
RPGs
The Ur Quan Masters (Star Control 2) - Encounter strange alien races, both hostile, friendly, and neutral, and travel through the galaxy fighting for freedom in one of the greatest games of all time. May not seem like a RPG, but it essentially is. http://sc2.sourceforge.net/
Freedroid RPG - The "best" open source RPG. Its a diablo clone where you play as a penguin that kills robots. http://www.freedroid.org/
Lips of Suna - ARPG where you play as an anime girl or guy beating up other anime girls/monsters/etc. Features nudity, character creation with breast sliders, multiplayer, physics, destructible environments, suicide bombers, etc http://lipsofsuna.org/
Egoboo - 3D isometric RPG. Sort of a cross between Zelda and a roguelike. http://egoboo.sourceforge.net/
Solarus engine Zelda clones - Pretty good Zelda games. http://www.solarus-games.org/games/solarus-team/ and http://www.solarus-games.org/games/community/
GNU FreeDink (Dink Smallwood) - Open source version of Dink Smallwood https://www.gnu.org/software/freedink/
OpenMW (Morrowind) - Requires original game data https://openmw.org/
Arx Libertatis (Arx Fatalis) - Requires original game data http://arx-libertatis.org/
Exult (Ultima 7) - Requires original game data. http://exult.sourceforge.net/
Nuvie (Ultima 6) - Requires original game data. http://nuvie.sourceforge.net/
GemRB (Infinity Engine) - Requires original game data. Plays Infinity Engine games like Baldurs Gate, Icewind Dale, etc. Can play through BG1, BG2 and IWD1, other games may not be completable. http://www.gemrb.org/wiki/doku.php?id=start
Falltergeist (Fallout 1 and 2) - Requires original game data. Still in development but playable to some extent. https://falltergeist.org/
Freeablo (Diablo) - Requires original game data. Still in development but playable to some extent. http://freeablo.org/
REGoth (Gothic 1 and 2) - Requires original game data. Still in development, many things not implemented. https://github.com/degenerated1123/REGoth
Stealth
The Dark Mod - The spiritual successor to Looking Glass Studio's Thief games, runs on the idTech 4 engine. http://www.thedarkmod.com/main/
TPS
OpenJK (Star Wars Jedi Knight: Jedi Academy and Star Wars Jedi Knight II: Jedi Outcast) - https://github.com/JACoders/OpenJK
TBS
UFO: Alien Invasion - 3D XCOM inspired game with singleplayer as well as multiplayer http://ufoai.org
Battle for Wesnoth - https://www.wesnoth.org/
Liberal Crime Squad - 3.05 and later are open source. Satirical political game where you manage the Liberal Crime Squad. http://lcs.wikidot.com/
Hedgewars - Worms clone http://www.hedgewars.org/
Scorched 3D - 3D Scorched Earth clone, takes place on randomly generated islands that are destructable. http://scorched3d.co.uk/
Advanced Strategic Command - Battle isle clone. https://sourceforge.net/projects/asc-hq/
Open XCOM (X-COM: UFO Defense) - Requires original game data to play. http://openxcom.org/
free heroes2 (Heroes of Might and Magic II) - Requires original game data. https://sourceforge.net/projects/fheroes2/
VCMI (Heroes of Might and Magic III) - Requires original game data. http://forum.vcmi.eu/portal.php
Autism simulators
OpenTTD - Transport Tycoon clone, has multiplayer and mods https://www.openttd.org/
Simutrans - Apparently more realistic than OpenTTD http://www.simutrans.com/
OpenBVE - Train driving sim, clone of BVE Trainsim. https://sites.google.com/site/openbvesim/home
Minetest - Minecraft clone written in C++ with a Lua modding API. I recommend using a "MC-Clone" subgame, the subgame the game comes with is barebones http://wiki.minetest.net/List_of_Subgames Also, the default textures are crap, I recommend this for a 32px texture pack https://forum.minetest.net/viewtopic.php?f=4&t=13327 or this for 16px https://forum.minetest.net/viewtopic.php?f=4&t=14132 Download the game here http://www.minetest.net/
OpenRCT2 - Its Rollercoaster Tycoon 2 for multiple platforms and with multiplayer. https://openrct2.org/
Flight Gear - General aviation flight sim http://www.flightgear.org/
The Powder Toy - Falling sands type game, you can create nuclear reactors, cities, functioning computers and more or just blow everything up in this fun physics game. Can load up other people's creations too, theres quite a few of them. http://powdertoy.co.uk/
Golems - 3D physics simulator. http://www.golemgame.com/
Space Nerds in Space - Cooperative multiplayer networked starship simulator. It requires some friends with computers and a projector/tv/big monitor. GNU/Linux only, might work on Mac. https://smcameron.github.io/space-nerds-in-space/
Race Into Space (Buzz Aldrin's Race Into Space) - Open source version of Buzz Aldrin's Race Into Space. http://www.raceintospace.org/
OpenRails (Microsoft Train Simulator) - Requires either original game data or community made game data. http://openrails.org/
CorsixTH (Theme Hospital) - Requires original game data. http://forums.corsixth.com/
CaesarIA (Caesar 3) - Open source engine that can run Caesar 3, a city-building game. https://bitbucket.org/dalerank/caesaria/wiki/Home
4X
Freeciv - Civilization 2 clone. http://www.freeciv.org/
c-evo - Similiar to Civilization. http://c-evo.org/ and http://www.c-evo.org/bb/viewtopic.php?f=6&t=147
FreeOrion - Master of Orion inspired 4X in space. http://www.freeorion.org
Open Imperium Galactica - https://github.com/akarnokd/open-ig
FreeCol - Colonization clone. http://www.freecol.org/
Roguelikes
Dungeon Crawl Stone Soup - https://crawl.develz.org/
Tales of Maj'Eyal - http://te4.org/
IVAN - Old version at http://ivan.sourceforge.net/download.html Development continued at https://attnam.com/wiki/Main_Page
Cataclysm DDA - The absolute premier post apocalyptic survival roguelike experience. Vehicle building/driving, crafting, construction, limb damage, bionics, mutations, weather, drugs, farming, and more. http://en.cataclysmdda.com/
NetHack - A classic. http://www.nethack.org/
Angband - A roguelike loosely based on Tolkien's works. http://rephial.org/
Brogue - https://sites.google.com/site/broguegame/
Pixel Dungeon - http://pixeldungeon.watabou.ru/desktop.html
GearHead 1/2 - Mecha roguelike/RPG game. You need to compile it to play new versions, binaries are ancient. http://www.gearheadrpg.com/
Prospector - Space game that takes place in a randomly generated universe that you can explore, land on planets etc. The goal is to get a lot of dosh and retire. The game is unfinished and it is not clear if development has ceased. http://www.prospector.at/forum/dm_eds/dmedsdl.php
Platformers
Sonic Robo Blast 2 - Gotta go fast https://www.srb2.org/
Open Sonic - Sonic the Hedgehog clone with a greater focus on switching between characters. http://opensnc.sourceforge.net/home/index.php
The Secret Chronicles of Dr. M. - Mario clone with level editor http://www.secretchronicles.de/
Neverball - http://neverball.org/
X-Moto - Motocross platformer, many user created levels http://xmoto.tuxfamily.org/
Frogatto - Commercial but open source. https://frogatto.com/
MMOs
Planeshift - http://www.planeshift.it/
Ryzom - http://ryzom.com/
OpenMeridian (Meridian 59) - http://openmeridian.org/
Darkspace - http://www.darkspace.net/
The Mana World - https://www.themanaworld.org/
Space
Oolite - A nice clone of Elite, has mods referred to as "expansion packs" which use the OXZ and OXP formats. http://www.oolite.org/
Pioneer - Space: the final frontier. These are the voyages of the Frontier: Elite 2 clone Pioneer. Its continuing mission: to explore strange new worlds, to seek out new developers and new artists, to boldly go where no space game has gone before. http://pioneerspacesim.net/
Vega Strike - http://vegastrike.sourceforge.net/
Naev - Escape Velocity clone. http://blog.naev.org/
Endless Sky - Escape Velocity clone. https://endless-sky.github.io/
Privateer Gemini Gold - Fan remake of Wing Commander: Privateer, uses Vega Strike engine. http://privateer.sourceforge.net/
VegaTrek - Star Trek fan game, uses Vega Strike engine. http://vegatrek.sourceforge.net/
Space Combat - Its like the potato cousin of Freespace. Has some really unwieldly menus, theres even a space battle going on in one. http://spacecombatgame.sourceforge.net/
AuroraRL - Space exploration game inspired by Star Control 2 and Prospector, older binaries available free of charge, newer ones are sold on Steam. https://bitbucket.org/e_smirnov/aurora/wiki/Home
Rhythm
Stepmania - DDR style rhythm game, highly configurable http://www.stepmania.com/
Frets on Fire X - Guitar Hero clone. Improves Frets on Fire significantly, but you need to compile it yourself on OS X and Windows. https://github.com/fofix/fofix
Ultrastar Deluxe - Karaoke game inspired by Singstar. http://ultrastardx.sourceforge.net/
Racing/Vehicles
Rigs of Rods - Vehicular soft body physics sandbox game, comes with a "rig editor" to make vehicles with. Features cars/trucks, trains, boats and planes, quite a few of the community made vehicles can be damaged. You will want maps/vehicles from the community repository, the game doesn't come with many. https://rigsofrods.github.io/
SuperTuxKart - Kart racer with the typical features, there isn't online play yet but its being worked on. http://supertuxkart.sourceforge.net/
Armagetron Advanced - The lightcycle sequence from Tron made into a videogame. http://www.armagetronad.org/
H-Craft Championship - Futuristic racing game, sort of like Wipeout. http://www.irrgheist.com/games.htm
Stunt Rally - http://stuntrally.tuxfamily.org/
Speed Dreams - http://www.speed-dreams.org/
Dust Racing 2D - Top down racing game featuring a level editor and split screen. https://juzzlin.github.io/DustRacing2D/
Tux Racer - A classic. Slide down snowy slopes as the venerable Linux mascot himself. https://sourceforge.net/projects/tuxracer/
Point n Click
Beneath a Steel Sky - Requires ScummVM to play http://scummvm.org/ Download the game files here http://scummvm.org/games/
ICBM - Realistic depiction of how a Nuclear and Missile Operations Officer's job would be like in the 1980s. http://gamejolt.com/games/icbm/57197
GameLV - Post Soviet adventure game. http://piepe.lv/game-lv/
Fighting
PainTown - http://paintown.org/
OpenOMF - Requires original game data. http://www.openomf.org/
OpenMortal - Parody of Mortal Kombat https://sourceforge.net/projects/openmortal/
Shooters/Shoot em ups
Gang Garrison 2 - A multiplayer 2D "demake" of Team Fortress 2. http://www.ganggarrison.com/
Teeworlds - Soldat meets Worms https://www.teeworlds.com/
OpenTyrian (Tyrian) - Vertically scrolling shoot em up where you can configure/upgrade your ship inbetween levels. https://bitbucket.org/opentyrian/opentyrian/wiki/Home
Shmupacabra - Horizontally scrolling shoot em up, shoot down ships and stuff. http://piepe.lv/shmupacabra/
Torus Trooper - Reimagining of the old arcade game Tempest. Windows version: http://www.asahi-net.or.jp/~cs8k-cyu/windows/tt_e.html GNU/Linux version: http://www.emhsoft.com/ttrooper/
Tumiki Fighters - Its the Katamari Damacy of shoot em ups! Horizontally scrolling shoot em up, when you kill enemies you catch them for points/more firepower, and they become latched onto you. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/tf_e.html GNU/Linux: http://tumiki.sourceforge.net/
Kobo Deluxe - Multidirectional top down shoot em up where you blow up space stations by shooting their core. Its an enhanced version of XKobo, which is similar to Bosconian. http://olofson.net/kobodl/
M.A.R.S.: a ridiculous shooter - Deathmatch style top down space shoot em up, with physics, pretty graphics, multiple modes, and local multiplayer. Development seems to have halted years ago, with the planned internet multiplayer feature still not finished. http://mars-game.sourceforge.net/
Mu-cade - Physics based 360 degree shmup, shoot centipedes and boxes off the table to get points and centipedes added to your tail. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/mcd_e.html The game appears to be in Ubuntu's repos.
rRootage - Vertically scrolling shoot em up boss rush, when the boss is killed a new boss is immediately created. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/rr_e.html GNU/Linux: http://rrootage.sourceforge.net/
Noiz2sa - Its an abstract kind of vertically scrolling shoot em up. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/noiz2sa_e.html GNU/Linux: http://noiz2sa.sourceforge.net/
Titantion - Vertically scrolling shoot em up with a capture/provocation beam, depending on the mode. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/ttn_e.html
Gunroar - Naval themed Geometry Wars type game. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/gr_e.html GNU/Linux: http://www.emhsoft.com/gunroar/
PARSEC47 - One of Kenta Cho's normal vertically scrolling shoot em ups. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/p47_e.html GNU/Linux: http://parsec47.sourceforge.net/
Blob Wars: Metal Blob Solid - Fun platformer/shooter where you play as a blob with a bandana who kills enemies, saves MIAs and completes objectives. http://www.parallelrealities.co.uk/p/blob-wars-metal-blob-solid.html
OpenLieroX - Liero clone. http://www.openlierox.net/
C-Dogs SDL - Old run n gun game from the DOS days, now open source and can be played on modern OSes. https://cxong.github.io/cdogs-sdl/
Project Starfighter - Currently only GNU/Linux builds exist. http://starfighter.nongnu.org/
Abuse - I don't know of an open source Windows or Mac OS X build, but its in some repos for GNU/Linux. http://abuse.zoy.org/
Puzzle
Rocks'n'Diamonds - Its Boulder Dash, Supaplex, Emerald Mine, and Sokoban all stuck in a blender to make one puzzle game. http://www.artsoft.org/rocksndiamonds/
PySolFC - Over 1000 solitaire card games http://pysolfc.sourceforge.net/
Frozen Bubble - Puzzle Bobble clone http://www.frozen-bubble.org/
Pingus - Lemmings clone http://pingus.seul.org/welcome.html
Enigma - Similiar to Oxyd http://www.nongnu.org/enigma/
Zaz - Zuma-like game http://zaz.sourceforge.net/
Hex-a-Hop - Hop on hexagons. http://hexahop.sourceforge.net/
Berusky - Sokoban-style game with a level editor. Theres a 3D sequel for GNU/Linux only. http://anakreon.cz/?q=node/1
Blockout 2 - Blockout clone, which was a 3D Tetris game. http://www.blockout.net/blockout2/
Tile World - Chips Challenge clone http://www.muppetlabs.com/~breadbox/software/tworld/
Fish Fillets NG - Improved version of the original Fish Fillets game. http://fillets.sourceforge.net/
Pushover - Clone of the original Pushover game, which was a domino puzzle game. http://pushover.sourceforge.net/
Arcade
A7Xpg - A "chase action" game where you grab gold while avoiding the enemies. Windows: http://www.asahi-net.or.jp/~cs8k-cyu/windows/a7xpg_e.html GNU/Linux: http://a7xpg.sourceforge.net/
OpenHexagon - Super Hexagon clone. http://vittorioromeo.info/projects.html