These tiny units project a virtual laser keyboard on your table. They are fully functional and even make those little clicky click sounds while you type (optional). It uses a couple of sensors to measure the shadows thrown by your fingers from the projected light in order to indicate their positions. There are several on the market now, including this one conveniently located on amazon. It is compatible with bluetooth and USB, most operating systems, mobile and otherwise, and runs on DC, battery, or USB.
One of the first things that occurred to me when I saw this is that someone needed to make one for DDR/Stepmania. Remove the need to store and stand on a giant mat. Apparently someone is at least partially on that trail (via Engadget), although the execution looks relatively weak at the moment.
Obviously we will be seeing a lot more of this kind of tech soon. I’m hoping in the near future laptops will come inside cellphones. Just drop it on the table and project a keyboard and screen. You could probably do that now with a pico projector, a good cellphone, and one of these.
You can purchase it at ThinkGeek Electronics.