The well known, at least for us geek’s, technology used in the movie Minority Report, which enables one to control and manipulate the user interface with your hand movements. Perceptive Pixel showcased their technology with this video (Direct link):
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Microsoft has also some ideas on how they see this technology evolve. They call it the Microsoft Surface technology.
And now, the latest contenders in this fascinating technique is Cynergy Labs
You can watch the demo video here.