PSA

This webpage from 2007 is the first place I saw the same fundamental board design: http://woodgears.ca/marbleadd/

Direct video link: https://www.youtube.com/watch?v=GcDshWmhF4A

The design in the two links above is fairly simple (I'd hate to see the patent office decide it was unique[ly patentable], for example), and so I doubt that this person from 2007 was the first to build it.

But I wouldn't be surprised if this particular design and video served as some serious inspiration for the linked product.

To clarify, I recognize that this system far surpasses the basic wooden adder I've linked. But the similarities are there.