Spotify - Map shows when two people play same song at same time
Netflix Party - Netflix Party is an extension for watching Netflix remotely with friends and family for movies nights with that long-distance special someone.
Playlist Machinery - Tools that help you create & organize your Spotify playlists
Metastream - Watch streaming media with friends
Magic Playlist - Get the playlist of your dreams based on a song
StreamParty - StreamParty is a watch communiry, that allows you to watch video streams in sync with the people you care about, on multiple services.