Last weekend Spotify hosted the Music Hack Day Stockholm 2013 at their office in Stockholm. In the end, 65 projects were built by 162 participants, using APIs from a variety of music services such as Echonest, Musixmatch, Soundcloud, Radio and Spotify among others.
Overall it was a great experience. This was my first hacking event where people from outside my company participated. My project was Extendify, a Chrome Extension that injects Spotify Play Buttons in pages where it detects info related to a track, album or artist. You can check it out on Github.