Here's a ranked list of the best open source video games. 
1. Battle for Wesnoth
2. Xonotic
3. FlightGear
4. SuperTuxKart
5. OpenTTD
6. 0 A.D.
7. Cataclysm: Dark Days Ahead
8. Unciv
9. Warzone 2100
10. Dungeon Crawl Stone Soup
11. Minetest
12. Mindustry
13. Hedgewars
14. The Ur-Quan Masters
15. OpenRA
16. Shattered Pixel Dungeon
17. OpenMW
18. Teeworlds
19. Endless Sky
20. Zero-K
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