Recently I've been messing around with 3D printing puzzles. Puzzles can be pretty complex, so additive manufacturing is a good way to fabricate the tricky shapes.
One "puzzle" that I want to showcase is this dice box I made. 5 rotating rings select the chosen code (in this case the first 5 digits of π). When the code is correct, the inner cylinder holding the dice can be removed:
As you can see, each ring can be changed to alter the code. Click here if you want to print one for yourself!