A fun, easy-to-use implementation of the conductor program (see http://www.musanim.com/tapper/ for an historical overview of this idea). Not a professional-grade tool, but a good introduction. I played through all the fugues in the first book of Bach's Well-Tempered Clavier --- I ALMOST know them well enough to do this perfectly (except, of course, for the ornaments; I almost never guessed those right). The one thing that surprised me: after playing for a while, my fingertips felt really bruised (this is on an iPad); I've played the piano for 54 years, and I've never had this sensation playing a real keyboard instrument.