The InternetDJ API opens this electronic music site to your app. Since 1997 (not a typo!) composers and fans have been able to share and mix music and videos. According to the API's website, requests are limited to 5,000 a day, responses are in JSON and an auth key is required.
One of the challenges with building an application these days is the number of dependencies that application will actually have on other applications. Ideally in order to know how that application will actually perform application developers would be able to test their application against the application it depends on running in production. The odds of that happening, however, are slim to none, especially if that other application is running as a cloud service that has to be always available to end users.