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.
BrachioGraph can be found on Twitter.
Documentation
Complete documentation for the project, with detailed instructions on how to build and use it