Slackbox - Spotify playlist collaboration through Slack
Jukebox - Collaborative music player
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Festify - Festify is a free Spotify-powered app that lets your guests choose which music should be played...
Exportify - Export your playlists from Spotify
Join My Playlist - Listen to music live together with your friends in Spotify.