The Think a Dot was a small non-electronic toy with an 8 pixel 2-bit display. To change the color of the pixels, you dropped marbles into three holes at the top.
As you can see, the pixels change color based on the current color of the pixels and which hole the marble is dropped in.
Someone has made a 3D model of the toy and uploaded it to Thingiverse, so you can 3D print your own!
Image: Decode Systems
