Rich Gain of Microcubology has made the worlds smallest puzzle(as far as I know). You can check it out here in his Shop. The puzzle is $9.95 and is 3.5 by 5.5 by 0.9cm and looks very challenging. Rich has made a video where you can see him playing with his puzzle below. You can solve it in two ways by building a cube or by building an "inside out cube" that is hollow on the inside. Pretty nifty, ya think?
This is a great puzzle, and feels sturdy enough to stand up to repeated assembly/disassembly. It took a bit of cleaning up with a toothpick to remove residual powder, but after that it was pretty easy to work with.
It isn't the smallest puzzle, though. Allan Boardman makes smaller puzzles, by hand, out of wood:
I do know about Allan's incredible pieces but I'm not sure how easy it is to buy them. That's why I always qualify my meager efforts with "smallest commercially available puzzle" and still add the question mark!
I think you can still get them from him by mail, but certainly not as easily. And not as inexpensively, either! I love that I can get a whole set of your mini puzzles for a quite reasonable price.
Also, many of his puzzles are too small to work with bare fingers, whereas yours are sized so they can be done without special tools.
I also enjoyed your tutorial on making printable puzzles with burrtools, I hope to give that a try myself at some point.