DID's (Digital Information Development) portable virtual piano lets you turn any surface into a musical keyboard. It uses "a red semiconductor laser module and holographic optical element" to project "a 25-key 2-octave keyboard onto the surface in front of it." Expect to shell out $130 for this gadget when it's released in November.
A CMOS camera module and infrared (invisible) red semiconductor laser module detect which keys are touched, and the corresponding notes are emitted from speakers built into the device. The keyboard has 3 other voices in addition to piano — organ, pipe organ and harpsichord