Spotify is a streaming music service. They offer a great developer API that can do all sorts of cool things, such as retrieving and updating playlists, finding songs, albums, artists. It can even analyzing songs!

Getting Started with Spotify

Start by registering for a Spotify developer account. Check out all the starters in the Spotify Glitch team. Select one that fits your app idea the best, and remix it. Follow instructions in the README and make something cool!

Learn more about how their API works by reading the docs.