When Steve Clayton happened upon a Surface computer in Redmond, he didn't just play with it, he filmed himself playing with it! And it introduced me to a Surface app I had not seen before - the "Grand Piano." This application simulates a piano keyboard while showing off the Surface's ability to handle multi-input. The app came from an existing app created by the Expression Blend folks as an example of WPF and was tweaked to work on Surface. (For the techie details on how that was done, check out the Surface Team's blog post here). To see the piano application in action, check out the video Steve posted here.
Microsoft, Surface, Piano