The Rhapsody iOS SDK by Rhapsody allows interaction with the API. In addition to iOS 6.0 or higher, developers need to register the application to obtain an OAuth key. Includes instructions to configure an audio session, track playback, and receive notifications. By Daniel Duda.
Peachnote is quite an innovative approach to music analysis. Developed by Vladimir Viro, a renaissance man who bridges the worlds of classical music and advanced mathematics, the Peachnote API provides the ability to search a large collection of public compositions by melody or sequence of chords.
Echo Nest's API already powers hundreds of music apps (e.g. MTV, Music Hunter, Pocket Hipster, etc.). With new enhancements to its API, Echo Nest looks to expand its reach beyond the music industry by "us[ing] music to drive non-music apps." Echo Nest added "Taste Profile Similarity" and an "affinity prediction" system to its existing platform. With the new features, Echo Nest hopes to connect music listeners to other listeners with similar tastes and predict behavior unrelated to musical preferences.