Koel - A personal music streaming server that works.
Gnoosic - Even if you don't know what you are looking for - gnod will find it.
Mood Listener - Handpicked playlists to fit your mood.
Musicroamer - A visual Pandora for discovering new music
Spotify - Map shows when two people play same song at same time
TasteDive - TasteDive recommends similar music (musicians, bands), movies, TV shows, books, authors and games, based on what you like.