HacKey determines what keys you prefer music to be in
What key do you prefer to hear music played in? Most people aren't aware of a preference in this regard, but you might be surprised to learn that there are some clear key-related patterns to your listening habits.
HacKey uses your Last.fm account to determine your favorite music based on a unique listing of your top 50 tracks by play count (both overall and for the last six months) and your last 50 "loved" tracks. It then queries the Echo Nest API to get the keys for each song, and presents it to you as a pie chart, along with the percentage split between songs that are in a major and minor key. Once the pie chart has completed populating, you can mouse over a given key to see song titles that are in that key.
Is HacKey particularly useful? Not really, but if you're enough of music junkie to be scrobbling your listening habits to Last.fm, you'll probably find HacKey at least as entertaining as I did. And if you happen to like rock music as I do, I'll bet your favorite key is A Major like mine was.