Scratch 2.0 (currently in Beta as of today 1/29/2013) allows the user to have virtual objects and use their webcam to interact with them. One example of this is a virtual piano keyboard which you can play:
See bit.ly/scratch2demo for a video showing how it can be used to play chopsticks.
To see this demo on the Scratch web site login at beta.scratch.mit.edu, see user dalereed and the program called "Piano".
