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.
The most popular video API is about to become more popular. As just announced by Googe's Jim Patterson on the YouTube blog, YouTube Everywhere, the YouTube API has just been upgraded with some very powerful new features.
Facebook is a great tool for being able to go back and reminisce of good times with your friends and everything else that's happened in your life. Pretty cool stuff, that Facebook. YearlyLeaf not only agrees, but figured that the moments of your life are important enough to get in print using the Facebook API.