John Proudlock has used a Raspberry Pi to control a vertically-mounted plotter that creates stunning artwork. Called InkyLines, the Raspberry Pi is used to read in a low-resolution image and then convert that data into movements of two stepper motors. The stepper motors control the length of two cords, thus moving the print head.
See it in action below and read more over on his blog. You can see some of the artwork produced over on Instagram.