- The document describes PlayAnywhere, a compact interactive tabletop projection system that allows touch interaction on any flat surface without calibration. - It works by using a projector to illuminate the surface with visible light while an infrared illuminant and camera detect touches. Image processing techniques like rectification and optical flow are used to identify touches and gestures. - The system aims to be low-cost, portable, easy to set up and use on any surface without calibration beyond the factory settings. This could enable mainstream adoption of interactive multi-touch technology.