Researchers from the University of Tokyo developed a sort of e-paper display by using heat-sensitive ink on photochromic paper. Using lasers, the ink can be erased, and an ultraviolet projector overhead can be used to "print" new pixels. This is very slow but the laser is quite accurate (can erase a point of 0.0001 inch in size). The idea is that this can be used for collaboration - where on can draw on a paper and later others can add or erase stuff: