Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
TrackStack - Easy Spotify playlist sharing and collaboration
Heartbeat - Listen to music with your friends together, on Spotify
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Join My Playlist - Listen to music live together with your friends in Spotify.
Slackbox - Spotify playlist collaboration through Slack