Poolsuite™ - The super-summer music player
Spotify - Map shows when two people play same song at same time
Tiny Mix - NPR Tiny Desk — mixed up, one song at a time.
DiscVibe - Create personalized and contextualized Spotify playlists
Magic Playlist - Get the playlist of your dreams based on a song
Ranked Records - Create Spotify playlists with all an artist's songs