Linux Tycoon:
http://lunduke.com/linux-tycoon/

Infamous kraut pedo game:
http://unteralterbach.net/index.en.html

FreeCiv - explicit:
http://freeciv.wikia.com/wiki/Main_Page

Scorced3d - Pretty nice (looks like Worms in 3D):
http://scorched3d.co.uk/

Visual novel with tactical elements. You are a captain of a space ship and your crew is full of qts:
http://sunrider-vn.com/sunriderpage/
https://github.com/vaendryl/Sunrider

Obligatory tux racer:
http://extremetuxracer.sourceforge.net/

Open Red Alert:
http://www.openra.net/

0AD:
http://play0ad.com/

Unvanquished tactical FPS:
https://www.unvanquished.net/

Annex RTS:
http://annexconquer.com/

Tales of Maj'Eyal:
http://te4.org/

Aquaria:
http://www.bit-blot.com/aquaria/

Gish:
http://www.chroniclogic.com/gish.htm

Lugaru:
http://www.wolfire.com/lugaru

Mr. Rescue:
http://tangramgames.dk/games/mrrescue/

Tesseract:
http://tesseract.gg/

Wolfenstein: Enemy Territory:
http://etlegacy.com/

Performous, rockstar clone:
http://performous.org/

UFO:Alien Invasion:
http://ufoai.org

Space sims:
http://pioneerspacesim.net/
http://vegastrike.sourceforge.net/

Simcity clone:
https://code.google.com/p/lincity-ng/

Corebreach:
http://corebreach.corecode.at/CoreBreach/CoreBreach.html

Astro Menace:
http://sourceforge.net/projects/openastromenace/

Arx Liberatis:
http://arx-libertatis.org/

Syobon Action:
http://opensyobon.sourceforge.net/

The Dark Mod: avoid updater
http://www.thedarkmod.com/main/

HomeWorld - visual fap novel:
http://homeward.renai.us/

Cyber FPS:
http://www.terminal-overload.org/

Frogatto, side scroller:
http://www.frogatto.com/

Pingus, Lemmings clone:
http://pingus.seul.org/welcome.html

Frozen Bubble, puzzle bobble clone:
http://frozen-bubble.org/

Hedge Wars, roms clone:
http://hedgewars.org/

ABA action games:
http://sourceforge.net/projects/tumiki/
http://sourceforge.net/projects/rrootage/
http://sourceforge.net/projects/ttrooper/