This is very similar to the Wii guitar but you could probably do more with midi.
Thanks crustea for the tip!
In addition to the traditional buttons, force feedback and the integrated mini-speaker, the true innovation is the presence of a gravity and acceleration sensor (the ADXL330, used in the army or automobile safety, for airbags systems) inside the Wiimote which collects the movements and acceleration of the Wiimote on each of the 3 axis, X, Y et Z.
The good news is that rather than using a proprietary protocol to transmit the infos from the Wiimote to the Wii, and then lock its hardware to keep an exclusive use of it, Nintendo has made the excellent decision (probably by commercial will) to use the Bluetooth protocol, standard of communication on PC and Mac for several years. This means that you can connect your Wiimote to your computer, and program it rather simply for any use you want.