Smart playlists apps

MickTagger — Alfred style keyboard shortcuts for Spotify

The app is like if Alfred was specifically made for Spotify; the app exposes a number of keyboard shortcuts to do common Spotify commands more quickly: add a song to a playlist, open a playlist, queue 3 more songs from the current artist, copy current song information (to share in iMessage) etc. The app also has a number of smart features: auto like a song when listening to it often, auto remove a song from a playlist after skipping it too often and a playlists organization feature called Mailbox Monday, that delivers new songs from playlists you choose every week.