There is this browser game (an idle/incremental one) about making paper clips. I realized that near the end of the game, you can take apart all your probes to make more paper clips. But then I started thinking about an efficiency problem. Because, you know, even if you use all the material from the universe and the probes, you still have the machine itself. So, maybe the best way to make paper clips with very little waste would be to create a nano-robot (not much bigger than the wire of a paper clip).