Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Slackbox - Spotify playlist collaboration through Slack
Twinjack - Stream Spotify music with anyone with just a link
Partyhero - Pass your friends the aux!
Parallel - Listen to music with friends over Spotify at the same time
Songmash - Create playlists with music that you and your friends love