rflickr is a Ruby implementation of the Flickr API. It includes a faithful reproduction of the published API as well as method encapsulation to provide more useful object mappings. rflickr features result caching to improve performance.
Recently, blogging service Posterous thought it would try and help ease the burden of moving from other places on the web to its blogging platform by developing a bunch of migration tools. All of these tools were built on other services' open APIs and designed to go in, grab your content, and republish it through Posterous maintaining as much metadata as possible. Things were fine until photo-hosting service Twitpic caught wind and cut of Posterous' API access.
Earlier this year, ProgrammableWeb reported that the New York Public Library (NYPL) had launched the What's on the Menu API, the first public API released by the institution. The New York Public Library has just announced the launch of the NYPL Digital Collections API which allows developers programmatic access to the Library's vast collections of digitized creative works including manuscripts, historical maps, rare prints, photographs and much more.