Jukebox - Collaborative music player
Slackbox - Spotify playlist collaboration through Slack
OutLoud Social Jukebox - Control the music with your friends in real-time
Partyhero - Pass your friends the aux!
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Songmash - Create playlists with music that you and your friends love