Playlist Machinery - Tools that help you create & organize your Spotify playlists
Spotify - Map shows when two people play same song at same time
Heartbeat - Listen to music with your friends together, on Spotify
Last.fm - The world's largest online music service. Listen online, find out more about your favourite artists, and get music recommendations, only at Last.fm
Partyhero - Pass your friends the aux!
SoundCloud - Enjoy music & follow favourite artists