Spotify is a streaming music service that pays artists royalties and uses
Facebook accounts for login. It has free (Ad-supported) or paid models, and has good integration and design
docs, which are avaialble at https://developer.spotify.com/technologies/apps/
However, it's difficult to find a good guide to building anything but the most basic app, so I put together
this three-part guide with working code demos, which walk you through building an app that displays playlists,
albums, and a song-of-the-day carousel.