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?
Garry’s Mod. There is a centralized location you can all get the relevent files from, or uploaf them to (Steam). Your game could be on a publicly accessable server. But, you are able to and pretty much must host the server yourself (or you could use a hosting service, but GMod won’t do it for you).