Playlist Hunt - Playlist Hunt is one of the best applications for Apple users to get the best music through it.
Parallel - Listen to music with friends over Spotify at the same time
Book Playlist - Collaborative music playlists for your favorite books
Slackbox - Spotify playlist collaboration through Slack
Musicon - An interactive music-making machine for children
Join My Playlist - Listen to music live together with your friends in Spotify.