The original server operated by the Mastodon gGmbH non-profit
It will be open source, end to end encrypted using Signal’s double ratchet encryption protocol, and he plans to make it easy for fediverse platforms to integrate it. The beta will release later this month.
I'm very excited for this too. The fact that the majority of the comments are not "ewww who whants ANOTHER chat client" really shows how much demand there is for something like that in this crowded space.