Complete list of FOSS games I tested

Multiplayer Games

• 0ad

  Real-time Strategy, Homepage
  Very much inspired by Age of Empires 2, but has interesting twists that makes it a own game. It runs good as long as the population limit is not set too high!

• Xonotic

  Arena Shooter, Homepage
  Quake/UnrealTournament-like shooter. I think, I don't have to say more xD

• Hedgewars

  Turn-based Strategy, Homepage
  2D Worms, just with hedgehogs ;)

• Teeworlds

  2D-Arena-Shooter, Homepage
  Mix between Worms and Quake

• Minetest

  Procedural Sandbox, Homepage
  Minecraft in open-source with little less content. Without modification it has no survival mode, just creative. BUT there are tons of mods out there, even one that imitates Minecraft with survival and crafting ;-)

• SuperTuxKart

  Arcade Racer, Homepage
  Mario Kart open-source xD

• Wesnoth

  Turn-based Strategy, Homepage
  Little bit like Heroes of Might and Magic

• Warzone2100

  Real -time Strategy, Homepage
  RTS game where you can design your own tanks

• armagetron

  TRON, Homepage
  A Tron clone, is it a own genre?

• OpenRA

  Real-time Strategy, Homepage
  OpenRA is a recreation of classic "Command and Conquer"-games

• Veloren

  Voxel MMORPG, Homepage
  Veloren is a procedural genereated voxel MMORPG

• Lichess

  Chess, Homepage
  Open-source chess!

Singleplayer Games

• Flare RPG

  Action RPG, Homepage
  Diablo 2-like

• Shattered Pixel Dungeon

  Rouge-Like, Homepage
  Best modification of the original "Pixel Dungeon"

• OpenTTD

  Transport Tycoon, Homepage
  FOSS tycoon

• Freeciv

  Strategy, Homepage
  As Civilization

• Tanks of Freedom

  Round-Based Strategy, Homepage
  If you see it, you know what's about

• SuperTux

  Jump 'n Run, Homepage
  Mario as a penguin