Bitsdujour have Beatunes 4 on special for $18.95 USD (normally $34.99 USD).
This is a new version of the software which has been getting some very good reviews and appears to be useful for those of us with large digital music collection and especially for DJs and other related professionals.
Here are a couple of such reviews -
http://www.djtechtools.com/2014/07/21/beatunes-4-semantic-na…
http://www.digitaldjtips.com/2014/08/review-video-beatunes-4…
Official website - http://www.beatunes.com/
And the blurb -
You know that your music collection could use a little attention. It's not enough just to have all of that music in digital format, you've got to have tracks, artists, and albums labeled correctly in order to find them, but who has the time to go through thousands of items? Certainly not you or I! That's why it's great to be able to automate this process using beaTunes!
beaTunes analyzes your music library, letting you fix incorrect information, eliminate duplicate files, discover orphaned library entries, and more! With beaTunes, what you thought would take days and weeks will be accomplished in mere minutes!
The wonder of beaTunes is just how powerful it can be. For example, beaTunes can automatically determine BPM and key for each of your songs, look up metadata and categorize songs — and that's before any error correction actually begins. When it comes time to actually fix incorrect items, beaTunes gets straight to work, detecting typos, incorrectly assigned genres, and more, not to mention finding duplicate files that clog up valuable hard drive space.
Once you've got a corrected, analyzed music library, you can use beaTunes to create matchlists based on songs that you specify, edit and sort existing playlists, even get harmonix mixing suggestions so that you can blow the crowd away at your next DJ gig!
It seems that another strong feature is the ability to create playlists based on a set of filters, from the website-
Creating playlists is an art
beaTunes helps you find the right songs for whatever playlist project you are working on. Starting with one song, it can suggest matching songs following your own rules—or even build a whole playlist.
It keeps the fun in creating something new: To set the mood for an evening, the pace for a run, or the beat for a night. beaTunes can help you get it right.