" Ever sing in the car? Maybe in the shower? You know who you are. Admit it, you like to sing, and you like music. Ever thought of writing your own music? Most people never get a chance to try... but we want to give everyone a piece of the songwriting experience, so we’ve developed Songsmith, an application that lets you create a complete song just by singing! Are we going to turn you into an award-winning songwriter overnight? Of course not. But Songsmith will give you a way to create something authentically musical and authentically yours, even if you don’t know the first thing about chords or music theory."
Check it out: http://research.microsoft.com/en-us/um/redmond/projects/songsmith/