Interesting. Do you know how they handle identity/usernames/contact discovery without central servers?
Torsten Grote, one of the projects main developers, explains the technology behind it in this very nice presentation: https://m.youtube.com/watch?v=Dr42vZIoGqM
The ability of TOR to allow essentially roaming services like this is a feature I'm always surprised isn't used more often. And although it's not something I was ever going to actually get around to, something like Briar has been on my list of interesting thins to try to do for a while -- I'm really glad someone else has had a similar thought and been able to run with it :).