From Music Hack Day
Reads your local iTunes library and indexes it with the Echonest. Exposes a control panel whih you can use to tune the parameters for your playlists. Plays in iTunes automatically - no streaming!
Ed Hickey Twitter
 About the hack
The key idea for this hack was to utilize a web API for deeper insight into local music collections. Web technology has opened up many avenues for musical exploration, but not all of them are ones you want to travel down. Most of the time, you simply want to better leverage your music, not take the rely on some "social recommendation engine" to provide your daily soundtrack. That's where Echotunes comes in. While it uses the excellent Echonest web API, all the music which is being analyzed, filtered and listened to comes from your local iTunes collection.
Echotunes sends your entire iTunes music library to Echonest and creates a "catalog". That catalog can be explored by a series of form controls (sliders, select boxes, toggles) in order to fine-tune a playlist. Want to hear energetic, minor key music between 120 and 128 BPM? How about a playlist which starts quietly, in the key of A and ends at full volume in the key of F? Echotunes can do that.
Although it is fully functioning, this was "just" a hack, so there is plenty left to do. Feel free to send pull requests!