The Social Networks Node.js SDK by Léo Pradel-Node is a meta SDK that serves as a social API client for node.js. It supports access, promises, and callback for the following social API's: Twitter, Tumblr, Facebook, and Instagram, as well as Github, via the same function calls.
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).
There is a new way to play FourSquare, the location-sharing game that just celebrated its first birthday. Kickball is an iPhone app that uses the FourSquare API (our FourSquare API profile) to let users check-in or see their friends. But it adds a few features that may have you leaving behind the flagship app that first made FourSquare so popular.