No kidding. Not counting games I play 'any way I can':
- Oolite
- Endless Sky
- Nethack
- Shattered Pixel Dungeon
- Dwarf Fortress
- Liberal Crime Squad
- Mindustry
- WarZone 2100
- OpenTTD
- OpenRCT2 (though this requires some investment, you need the files from the original 2 games)
- FreeCiv
- EDOPro
- Card-Forge
That's just what I have on this machine. If I check my GOG account, I'd have more. And I don't give money to Valve.