BrachioGraph - the cheapest, simplest possible pen-plotter
BrachioGraph is an ultra-cheap (total cost of materials: ~€14) plotter that can be built with minimal skills.
At its heart is a Raspberry Pi Zero and some relatively simple custom software, driving three servo motors.
The mechanical hardware can be built from nothing but two sticks, a pen or pencil and some glue. No tools are required.
Almost everything required can be found in a desk or kitchen drawer. The entire device can be built with no special skills in about an hour.