The Meetup NodeJS SDK allows to access community features that aim to extend invitations in social media applications. Examples available on GitHub present events, RSVP, groups, and photos. Additional samples at https://github.com/jkutianski/meetup-api/tree/master/examples
For over a year developers have been asking for an API from Quora, the Q&A site that has recently exploded in popularity. The company had been waiting until there were "enough users and content on Quora." A browser extension outed the interface and now there is an officially released, but still alpha Quora API.