I imagine the number of simultaneous connections is strictly limited.

For example, can multiple people message one person at the same time?

I'm thinking of local communication among groups of co-workers.

Reminds me of https://briarproject.org/

There is too much communication on what Berty doesn't do, and not enough on what it does.

So can it send messages over a network? Do messages have to be sent over a direct connection to the recipient's hardware? If messages can be carried by an intermediate, then who, when, and how? It would help a lot to answer these questions more immediately.

What's different about this one compared to Briar, Tox, Scuttlebutt, Cabal.Chat, NomadNet or Chitchatter (to name a few)?

IMO peer-to-peer chat is a mostly-solved problem. I think the problem that needs addressing is not lack of peer-to-peer technology, but lack of adoption. People (mostly) don't care, so they (mostly) won't switch unless you strong-arm them in some way or another, or convince them to care. And either way, if they're not close to you, you basically have no influence on them, so you still end up needing to use non-free, non-private modes of communication. Network effects are rough.

Does this support group chats? How does it do encryption if so?

I like the "Hey why don't you put your email address in our central database that authorities might find useful when they raid us?" form at the bottom of that page...