I have noticed that there are a few LEGO pieces that also function in the "real-world." For example, the 10830c01 Magnifying Glass can actually magnify.
Another example is the 70001pb01 Compass, which works the same way you'd expect any "real-world" compass to function. (Although it's not always 100% accurate.)
Are there any other LEGO pieces that have "real-world" functionality?
There appears to be a bit of ambiguity regarding what quantifies a "real-world" use. I suppose the line between a "real-world" use and not a "real-world" use is a bit hazy, so I am going to attempt to clear this up. Firstly, it should be noted that this question is primarily asking about individual pieces. (Theoretically, you could make most anything with enough LEGO pieces.)
I think it is best to look at the overall intended purpose of the piece.
What is a LEGO Magnifying Glass for? Well, after a toy, it is for magnification. What is the intended purpose of, as Aziraphale mentioned, LEGO Power Functions Motors? To motorize. On the other hand, what is a LEGO hinge intended for? To... serve as a door hinge? No. It's to be a small, LEGO compatible, hinge. "LEGO compatible" are the two keywords here. Could you use a LEGO hinge to serve in the "real-world?" I suppose you could, with a lot of modifications, after which it would no longer be just a LEGO hinge.
Here are a couple more examples:
- What is a LEGO wheel's intended purpose? To be a wheel for a real car or even a toy car? Nope. It's to be a LEGO Compatible wheel for LEGO axles and LEGO toy cars.
- What is a LEGO door piece for? To be a "real-world" door for people? No. It's to be a LEGO Compatible door.
- What is the purpose of a LEGO compass? To point North. Thusly, it would function in the "real-world."
- What is the LEGO whistle's intended purpose? (As Uli mentioned) To be a whistle.
Lastly, please keep in mind that the quantification of "real-world" usability is more of a spectrum and not a "yes/no" system.