open source games

xonotic: a fast-paced first person shooter similar to the quake and unreal tournment games.
openra: n open source clone of the command & conquer games.
battle of wesnoth: a turn-based strategy game with a good campaign.
supertuxcart: a mario kart type game with open source mascots instead of nintendo characters.
nethack: a roguelike game where you explore a dungeon to try to optain the amulet of yender.
dungeon crawl stone soup: a roguelike game where you explore a dungeon to try to potain the orb of zot.
freeciv: a open source clone of the civilization games.
openttd: an open source clone of transport tycoon deluxe
flightgear: a flight simulater with a lot of planes to fly.
hedgewars: a open source clone of the worms game series.
minetest: a open source clone of minecraft.
zero-k: a rts game with robots and stuff
sonic robo blast 2: a cool 3d sonic game
endless sky: a cool space trading combat game.
freedroidrpg: an open source rpg where you play as the linux mascot tux

freeware games

which: a short horror game where you have to find a way out of the house
the white chamber: a point 'n click horror adventure game set in space
yume nikki: a surreal adventure game where you play a little girl that explores her dreams.
cave story: one of the best games you will ever play.
i wanna be the guy: a very hard adventure platformer game with a lot of video game references
knytt: a game where you explore the world and find parts of a ufo
super crate box: a arcade shooter where you survive waves of enimies
barkley, shut up and jam: rpg where you play as famous NBA player charles barkley and save the world
Katawa shoujo: a visual novel about girls with disabilities
battleships forever: a tactical strategy game where you command a fleet of spaceships
enviro-bear 2000: a game where you play a bear driving a car
pirate bay bundle: a torrent with a bunch of weird little games in it
irisu syndrome: a cool japanese puzzle game with a cool story.(english patch: patch)
warning forever: a shmup with only bossfights.each boss learns from the last boss you kill.
TUMIKI Fighters: a shmup with adorable ghraphics
Photopia: a interactive fiction game with a interesting story