0.A.D., Veloren and Xonotic are my favorites. Also Sonic Robo Blast 2 is freaking awesome
Gaming
From video gaming to card games and stuff in between, if it's gaming you can probably discuss it here!
Please Note: Gaming memes are permitted to be posted on Meme Mondays, but will otherwise be removed in an effort to allow other discussions to take place.
See also Gaming's sister community Tabletop Gaming.
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Pokemon Auto Chess. Literally what the name implies, a Pokemon auto battler fan game. Honestly it's really well-polished for something only a couple of people are working on (aside from commissioned sprite artists) and has an active community to go with it.
I like supertuxkart and minetest
0 A.D. and Beyond All Reasons for me ^^
Arguable if you can call it a game or not, but there is Overte. It is an open-source social VR platform. (without crypto so please no pitchforks)
As one of its developers I might be biased, but I wouldn't be one of the developers if I didn't honestly believe in the project.