Last time I checked briar had no store and forward so both people have to be online or connected at the same time to chat. Ssb does privacy and store and forward which is really cool. We could totally add support for that in nostr easily.
Another example that works decently well is Briar. Briar allows connecting over Tor, local wifi or Bluetooth and it has concept of sharing posts across multiple people. I used it e.g. to chat with another person during a flight without internet connection...
https://briarproject.org/ #briar
Discussion
They have new concepts that allow sharing across multiple hops, but I haven't explored it yet.
https://code.briarproject.org/briar/briar-spec/blob/master/clients/Blog-Client.md