Music mix sharing site 8tracks now has an 8tracks API to search and play mix tapes. Developers can access the mixes, which each contain at least 8 tracks, by tag, simple search, popularity, those added recently, or randomly. The site announced its API at the recent Music Hack Day Boston.
The 8tracks service is a collection of mix tapes with a twist. You search for tracks, or even see which songs are on a mix. ReadWriteWeb explains why:
Because 8tracks songs are not identified prior to play, the company is treated as an internet radio station. This status as a radio station means that it avoids the high licensing fees plaguing the streaming music sites.
The Hack Day produced over 30 projects, though it's unclear whether any use 8tracks. Popular music APIs are SoundCloud and Echo Nest. 8tracks itself maintains a list of applications in its app gallery.