Mick Tagger is a music playlist organizer. You can use Mailbox Monday to group any number of playlists together by feeling, genre, artist, year, and whatever criteria you may think of.
Another smart feature is the Evergreen Playlists. The app will figure out which songs you skip often and which you play all the way through. After you’ve skipped a song enough times, the app will remove it from the playlist, so you’ll enjoy your playlists on every listen.