Pubsubhubbub is described as a simple, open, servertoserver webhookbased pubsub publishsubscribe protocol as an extension to Atom and RSS.

This is a protocol that Google itself has adopted for shared items in Google Reader, which allows it to contribute to realtime search. Google recently provided the following presentationThe PubSubHubbub protocol is decentralized and free, explains Six Aparts Nima Badiey. No single company controls it and anybody can run a hub, ping publish or subscribe using open hubs.The new TypePad PubSubHubbub hub builds on the exciting work that Brad Fitzpatrick a Six Apart alum and Brett Slatkins team at Google have done with the implementation of PubSubHubbub, Badiey says.