Way back in the day there was a fantastic piece of software from Brøderbund (of Lode Runner fame, among others) called The Toy Shop [0] that let you print customized papercraft designs that you would then assemble into working toys. Some of them were quite impressive - a steam shovel, a balloon-powered dragster, a mechanical clockwork bank, even a model steam engine!
It is still one of the most unique and creative pieces of software I've ever seen. I guess maybe it didn't do that well, though, since there's unfortunately not a lot about it on the Internet now. There is a copy in the Internet Archive [1], though.
It would be an interesting project to resurrect this, or at least extract the models into a modern format.
I seem to remember Microsoft Fine Artist having a lot of cool clip art you could print and fold into specific things