This is a mechanical binary counter, helpful while learning the basics of counting with binary. I got the idea from this Reddit post, and all credits to the original post for the general design, while the 3D models are mine.

This system is expandable as far as you want it, but for each "bit" you want to display, you need to print one "Number_Card.stl", one "Peg.stl", one "Flap.stl" and one "Stand.stl". For the last bit, however, you only need to print a stand, number card and "End.stl"

My simulation shows a two bit counter without all of the bits cuz I'm lazy, but it should show the general setup for the counter.

My design is optimal, as it requires no additional materials other than the 3D printed parts, other than maybe superglue if you want it to be more permanent

I have not printed this yet, so there may be problems with it, however feel free to download it and try it, and give me some feedback!