Minetest and several others that I play regularly have already been mentioned, so I wanted to shout out a game I’ve been following and playing for years, waiting for their 1.0 release: FreeOrion

https://www.freeorion.org/

It’s essentially a clone of the Master of Orion series, which are classics in the 4X world.

That seems… Not great.

You could determine which XEPs to support…? Also, the usual benefits of hosting your own services. But neither is really a strong selling point IMHO.