Brain made a computer controlled cookie frosting robot, he writes -

The Frost Bot robot consists of a small table-top CNC router kit made by www.fireballcnc.com, augmented with a forth axis stepper motor driving a frosting extrusion device. The four stepper motors of the system are driven by a single board called a Quad EasyDriver, which is based upon putting for Easy Driver boards together and sending them data using two shift registers. (Like a one-directional SPI bus.) This board is driven by a UBW controller board (from SparkFun) using a custom firmware and powered with a standard computer (AT) power supply at 12V. The UBW firmware takes motor move commands over the USB connection from a computer. The computer runs a Liberty Basic application that loads HPGL based vector graphics files, and sends them to the UBW. It also handles homing, jogging, zeroing, offsets, etc. The HPGL input files to the Frost Bot software are generated from Post Script files using GhostScript, and those .ps files are generated from SVG files made in InkScape. Although it all sounds really complicated, it is actually straightforward if you think about each chunk.

FrostBot – a CNC robot for frosting cookies – Link.