Gentlemen, welcome to the Holodeck. A team of Japanese scientists has finally created holograms you can touch.
Using ultrasonic waves to provide the resistance and tactile presence, the hologram simulates the sensation of rain drops or a small ball, all without interfering with the projected 3-D image. A couple of Wiimotes provide the tracking, and the programing provides the fun.
There's really nothing I can write that will be as cool or explanatory as the video above, so you might as well just start walking it while you day dream about a veldt or Danger Room of your own.