The document describes the sixth sense technology, which allows users to interact with digital information projected onto physical surfaces using natural hand gestures. It was pioneered by Steve Mann in the 1990s and later refined by Pranav Mistry at MIT. The system uses a camera to track colored markers on the user's fingers and a projector mounted on a neckpiece to display interfaces onto any surface. It has applications like making calls, using maps, taking photos, and obtaining information about objects.