Video game idea - with a handful of sensor devices (just like the Wiimote or Nunchuk controller), one could learn karate. Put one in each hand, and one on each ankle, to start with. They wouldn't have to have buttons or anything, just be capable of tracking motion. Expert mode might also be used with shoulder and knee sensors. After learning certain moves, and practicing kata, the player could test himself in a match with a virtual opponent. It might seem like a game, but the real goal here is to teach karate as a form of self defense and physical/mental fitness. Other martial arts might also be adaptable - kung-fu, taekwondo, etc. Look at all the shitty exercise games that are coming out to compete with Wii Fitness - this would be 100x cooler than that, and still help with cardiovascular health and provide a fitness routine.
