I've been building a board game community on ATProto. The idea revolves in trying to build the feeling of local clubs but online, instead of "PLAY NOW" being on the landing page (although you can play now if you want) it's organized around clubs. I also wanted to move away from one game oriented community. I play Go and Chess and I would love clubs to be for mixed games. You can create leagues, or tournaments, etc.

As an extension of that I've been building a small language to build games (with a nice time traveling debugger and automatic replays) inspired by Elm. Go and Chess are both built on top of this and you could fork them and modify the rules. Want to code a new Chess variant? Go ahead! Want to code a whole new game you want to try? Go ahead!

What I'm very excited with ATProto is that because all games are broadcast on it and each shares a core system of turn-based replays (and review system with branching) software can be built on top to do AI analysis, or a replay view. The idea that my application can be extended without me adding an API is very exciting and very much in the direction I want to take the system (community is the core tenet).

How do you prevent a player from manipulating game state outside of the app view?

There is a subgroup in the Atmo working on games, have you found them yet?