Heartbeat - Listen to music with your friends together, on Spotify
22tracks - DJ curated Spotify playlists on iOS
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
BandNext - Discover bands that sound similar to artists you already love with BandNext. A single click saves your results to a Youtube playlist.
BeatSense - Discover great music hand-picked by real people, in a single click. FREE and in real-time!
Spotify - Map shows when two people play same song at same time