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.
Great news that it will work across the fediverse. I'd love to try pixelfed for example, but its got too much of a walled garden thing going on since nobody I know uses it.