At the time federation was not that special. E-Mail was federated and Jabber/XMPP was federated too. So it was expected, that the successor (as which Wave was marketed) of e-mail was federated too.
The real time aspects, on the other hand, were pretty amazing at the time. From todays perspective the reverse might be true ;-)
The underlying architecture was federated; basically an XMPP extension. When Wave shut down, they handed the federated server code to the Apache Foundation, who briefly developed it under the name "Apache Wave". Apache Wave was shut down in 2018, but you can still download the code.
The real time aspects, on the other hand, were pretty amazing at the time. From todays perspective the reverse might be true ;-)