The Swipp API allows developers to integrate Swipp's "Social Intelligence" into their sites and applications. Public information is not available on the API; interested parties are asked to email email@example.com. Once available the APIs will "make it possible for people to interact around any topic imaginable."
Hellotxt, the service that lets you simultaneously update your status and read your friends' status across many services, has now released an API. There is a long list of microblogging and social networking sites that Hellotxt interacts with, ranging from Facebook and LinkedIn to of course Twitter and FriendFeed (see their home page below).