For much of recorded history, permanent printing involved the staining of paper with ink. Towards the latter half of the 20th century, papers pre-embedded with chemical capsules that burst with the application of heat or pressure were available, but even that involves ink in a roundabout way. Inkless means of recording with paper have emerged, such as with braille embossing or paper computer tape or card punching, but higher definition imagery or text recording without ink has been elusive.
"Printing" with a laser engraver and cutter is interesting to me because it is a subtractive process that does not require ink; the laser can etch at a high power and make marks with minuscule burns, and it can vaporize away the top, darker layer of multilayered papers of differing contrasts for even brighter images.
Combination laser cutters/engravers are even more exciting for bookmaking because the problem of registration between paper, printer and binding methods are eliminated: From a raw sheet of paper, the text or images can be imprinted, an exacting size of a page can be cut out, and holes for binding can be cut all in one action from a single computer file.
As an example of this emerging possibility, I've made an animated flip book; the applications of inkless printing need not be limited to static text or images.