Slackbox - Spotify playlist collaboration through Slack
BeatMix - Enables Shuffle and Radio for multiple artists in Spotify
Partyhero - Pass your friends the aux!
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Songmash - Create playlists with music that you and your friends love
aux.app - A free web-based music platform to play music from other popular online streaming services.