Coloring computers: non-electronic computers that work when you color them
This made me imagine an educational toy that allows you to make <i>working</i> simple circuits by drawing: You draw with markers that have electrically conductive ink, then touch the contacts of a 9-volt battery to your drawing at a certain point and a bulb or LED that you've taped to your drawing lights up. Maybe you'd supply prefabricated stickers that contain logic gates that you stick to the paper where you need a gate.