Spotify - Map shows when two people play same song at same time
Slackbox - Spotify playlist collaboration through Slack
Tycho Forecast - Turn your weather into a Spotify or Apple Music playlist
Partyhero - Pass your friends the aux!
SpotiMy - Play/Pause and Next/Previous functions for Spotify directly on your Menu Bar!
Songmash - Create playlists with music that you and your friends love