I've used cornychat quite a bit, but not sure if that meets all your needs.
They require users to create an account.
Eventually NOSTR Nests could work instead.
nostr:nprofile1qqsf5tw68y8ahj8njvh0agu4yx2al6cdn83edzmxcdh47dewucd0gcqa8tlah was tinkering with that last weekend.
We may start using that at some point.
I've used cornychat quite a bit, but not sure if that meets all your needs.
No replies yet.