- Dwarf Fortress - colony sim
- CDDA - rougelike
- FreeDoom - Doom port, compatible with most mods
- Lugaru - ninja rabbit fighting
- Minetest - minecraft clone
- Super Tux Kart - racing game
- Daggerfall Unity - rpg
- Pathos - nethack clone rougelike
- Endless Sky - space sim
- Hedgewars - worms like game with hedgehogs
- Battle for Wesnoth - strategy
- ColoBot - programming puzzle game/rts
- OpenTTD - transport tycoon
- Shattered Pixel Dungeon - rougelike
- Mindustry - like factorio but more tower defense
- 0.A.D - rts
these are the ones i've tried
oh and keep an eye out for Kitten Space Agency