• 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