Facebook Developer API

Social networking site Facebook has opened up access to its service via a set of RESTian APIs, giving developers access to a user’s profile data, friend list, inbox, calendar, photos, blog posts, and more. The Application Programming Interface (API) could be used to create a desktop or mobile version of a user’s Facebook data or easily migrate them to a new social network, photo site, or calendar. (via GigaOm)

Web applications are limited to 100,000 requests a day and desktop applications are restricted to 5 requests per second.