Idupe - iTunes has a “Show Duplicates” command, but it is of limited use.
Mixed in Key - Mixed In Key is award-winning DJ software that gives you the #1 technique of the world's best...
Tune Sweeper - Show duplicates in your Music library. Automatically select which duplicates to keep and delete based on your preferences. Remove duplicates with one-click from your iTunes or Music app library.
beaTunes - Smart software for library management, music analysis, and playlist creation. For Windows and macOS.
Leawo Tunes Cleaner - Leawo Tunes Cleaner is a powerful iTunes cleanup tool, which can help you to delete duplicates in iTunes and get album artwork for iTunes music files.With it,you can clean up iTunes music library fast and comprehensively.
Tunebat - A browser based song key and bpm database. Supplies compatible songs for harmonic mixing.