You know how Spotify (or any other service) will just silently remove tracks from your playlist because they lost the rights? No notification, a beloved song just disappeared from your life.

Building a webapp to keep track of your playlists and notify you when a song disappears

https://github.com/thehappyidiot/save-my-music

Support for Youtube playlists please... having to lookup the watch ID on Google after a song is removed to guess what the track was is a highly sucky part of using Youtube for music.