Rdio Web Service PHP SDK by Rdio helps developers to authorize with OAuth. A basic example presents basic API set up and API call. Rdio has been recently acquired by Pandora. For integration updates, follow @Rdio on Twitter.
Twilio has introduced two new APIs for enabling multi-user augmented reality (AR) applications; the DataTrack API and the Media Sync API. The APIs allow developers to build apps that provide a more immersive environment for users and an AR experience that immediately reacts to changes.
The Independent Online Distribution Alliance (IODA) has just announced its IODA Open API, currently in beta. The API offers many of the typical resources that you would expect from a music metadata service, with a few extra goodies like these album attributes: UPC code and primary label. Comparing album API results between IODA Open and iTunes, IODA is packing a lot more information into the response.