Tech Fridays: PubSubHubbub
PubSubHubbub is a "simple, open, server-to-server web-hook-based pubsub (publish/subscribe) protocol as an extension to Atom (and RSS)." Although the presentation below isn't the most lucid, PubSubHubbub and other work in this area such as XMPP can be thought of as adaptations of the well-known Observer Pattern to a network.