There was the Locker project by Jeremie Miller (XMPP), but it failed to gain traction and I think he pivoted into a more small scale commercial effort with it I

There was the Locker project by Jeremie Miller (XMPP), but it failed to gain traction and I think he pivoted into a more small scale commercial effort with it IIRC. The telehash protocol of Locker was extremely interesting.