I chose to do a stacking rings toy, but I added a small modification to the original idea. I added two specific areas on the rings that only allow them to fit together correctly when they are lined up, as opposed to just stacking them.
I think this toy is very suitable for the toddler age group. It not only has modifiers on the rings to teach proper ordering systems but it also has a specific alternating color scheme. Not that the color scheme is vital to the stacking rings being correct but it does help with understanding order.