UJAM opened their tools to the public in the open Beta. If you like to toy around with music and interesting tools you sure should give this one a try!
Basically it does this: You upload or record an audiotrack of either a singer or a single voiced instrument and UJAM then will analyse it and create a backup track for it. The result is quite good - check out the example track I made:
I took a piece from Carmina Burana (I can't really sing myself) and just removed the orchestral and choir bits (since the tool can't work with chords ind the raw material), selected a style for it and went past all the additional tweaks right away - this is what I got. :)