Is there anything like this? Something like Roblox, but rather than using a central server, using a network of decentralised servers with different self-hosted instances (a bit like the fediverse, but for online multiplayer games)
If there’s nothing like this, how difficult would it be to start something like this myself?
edit: Or maybe something like Scratch, where you’re not tied to a specific movement system and can program whatever kind of game you want?
I believe Space Station 14 fits your criteria exactly if I’m interpreting it correctly. Space Station 13 would as well if not for the fact that player accounts must still be centralized to a server. That server is currently under a cyber attack, which really shows the importance of decentralization (in this instance, I’m not that big a fan of the concept).
Further edit: after reading your other comments, definitely try out either SS13 or 14. I don’t play much these days because server variety has fallen off a cliff but the idea is all sorts of communities pop up with their own server which could deviate heavily from wherever they forked from. This led to all sorts of different playing experiences. Try some out to see if they fit your preferences.