APIs continue to work their way into just about every part of the digital economy. The latest example is Subledger, which offers a suite of APIs that let developers integrate accounting functionality into their applications.
Stereomood is a streaming music service that gives recommendations. To start, it uses a list of moods, each of which have an associated playlist. While playing songs, users can like or ban songs, much like Last.fm or Pandora. The Stereomood API allows full access to the site's functionality to developers, allowing developers to make fully usable clients on any platform.