I recently thought of a webtoy/interactive thingie from some years ago. It was fairly simple in operation and design. The graphics were also simple, just lines and curves. It allowed you to draw gears/wheels whose diameters were an integral number of units. You could stack a smaller gear/wheel on a larger one, then have a separate and larger gear wheel mesh with that, allowing huge reductions. You could also connect the gears/wheels with belts. Then you’d click to see your entire construction in operation.
I’ve tried Google without success.
Sound familiar to anyone?