foursquare2 is a Ruby wrapper for version 2 of the Foursquare API. Users will need to implement the OAuth2.0 gem as well, since the foursquare2 gem doesn't handle the API's OAuth 2.0 authentication flow.
Queeky is an interactive online drawing community for lovers of drawing and online art. The platform provides special drawing tools for users to create their own masterpieces and also showcases work from a worldwide collection of creatives in its galleries. The QueekyPaint API makes it possible to add this data to personal blogs and websites.
Gnip's Audience API promises to let brands and marketers glean real-time, in-the-moment data about audiences that convalesce around topics, events, or other users. The idea is to give companies as much information as possible about those with whom they might want to engage.