From the announcement:
"MySpace, the world’s largest social network, and Google, Inc. (NASDAQ: GOOG) today announced that they are joining forces to launch OpenSocial — a set of common APIs for building social applications across the web. The partnership spearheads an initiative to standardize and simplify the development of social applications. Today’s announcement underscores MySpace’s commitment to supporting standards that foster innovation in an increasingly social Web."
An impressive list for a start already ...
Google Announcement 'Google Campfire One'
Open Social Maka-maka (with Force)
If Facebook likes its member, application developer and/or is wise, they will joint and announce soon, that they have implemented that API's ... (and offer some convincing 'middleware' for the pack).