Wikipedia
OStatus
OStatus is an open standard for distributed status updates that references a suite of open protocols including Atom, Activity Streams, PubSubHubbub, Salmon, Webfinger, that allows different messaging hubs to route status updates between users in near real-time.
OStatus federation was first possible between StatusNet installations, and later between StatusNet and MiniMe. Various other content management systems are still incomplete in their compliance to the full standard.
In January 2012, a W3C Community Group has been opened to maintain and further develop the technology. There has been no progress made since then.