This could go in Howie Didits, I suppose, or under kid's magic, but I figured I put it where most of the cup threads are.
The Magical Child just had her 6th birthday and got lots of new Play-Doh. As we were cleaning out her old stuff, I noticed that that larger size, yellow plastic cups for Play-Doh stack quite nicely with room for about a 3/4 inch ball at least. The bottoms/tops even have a dimple.
With the labels left on, one could use colorful balls of Play-Doh and do a cups and balls routine for children.