Some time ago it was proven than LEDs can work as light source and as detectors. This time this effect was scaled to 64 bi-color LED matrix. The project called doodler enables drawing with laser pointer directly on matrix where each LED responds with one of two colors.
Circuit is built around Atmega48 which senses photo-effect current and controls LEDs using latches. This technique opens new area of game development or simply building larger scale interactive displays.