RDFa

Yesterday Facebook announced Opengraph:

The Open Graph protocol enables you to integrate your web pages into the social graph. It is currently designed for web pages representing profiles of real-world things — things like movies, sports teams, celebrities, and restaurants. Once your pages become objects in the graph, users can establish connections to your pages as they do with Facebook Pages. Based on the structured data you provide via the Open Graph protocol, your pages show up richly across Facebook: in user profiles, within search results and in News Feed.

Opengraph uses the Open Graph Protocol, which uses RDFa and “enables any web page to become a rich object in a social graph. For instance, [...] it enables any web page to have the same functionality as a Facebook Page.”

Initial publishers using Open Graph Protocol include IMDb, Microsoft, NHL, Posterous, Rotten Tomatoes, TIME, and Yelp.