I don't have anything written out, but this is how it works in Eve (my community building platform):

- each community is actually a nostr public private key pair

- users run their own relay (built in to the application)

- when they publish a note, it gets saved first to their local relay, then it gets encrypted (using nip44) and published to a bunch of relays, and using a PoW specified by the community

- the relays of other members of the community pull automatically any note sent to the pubkey of the community, and if it has enough PoW (to prevent DoS), attempt to decrypt it, and if it can be decrypted, they store it in their own relay

this has some issues right now:

- all members of the community have full access

- there's no way to kick anyone out

- every member will know the private key of the community

- a compromised key results in the whole community being compromised

I'm currently in the process (almost done) of rewriting this to use MLS instead of just having one key for the whole community, which will solve all the issues I outlined, but the current way it works is perfectly fine if those cons are reasonable for your use case