Songsmith functionality

Anyone know of a plug-in or Mac equivalent software that we can do to give Garageband the same functionality/abilities as Microsoft's new Songsmith software?

http://i.gizmodo.com/5128182/microsoft-songsmiths-corny-musical-infomercial

Would be fun to crank out songs using key and melody detection. I wonder how well it really works.

Anyone know how to do this on Garageband? I know you could run the software in "virtual" mode, but I'd like to see if there is a native version that then allows you to edit the song later on, or even change key and chords.