Cooking pots overheated I was boiling water in two pots, presumably stainless steel. I got distracted and the pots completed overheated and dried. After cooling down the pots, I find them both have brownish grey residual inside (I don't care about the outside), and one of the smells strange. Are they still safe to use? Thank you!
Yes, they are still safe to use. You aren't going to be able to heat them to the point where the metal starts breaking down — at least, not without starting a fire. 

Your only concern might be if your pots have a nonstick coating, which can be damaged above temperatures of 500 F and begin emitting noxious fumes. According to DuPont:


  The fumes that are released by overheated [Teflon coatings] can produce symptoms referred to as "polymer fume fever" — flu-like symptoms that are relatively quickly reversed in humans.


The residue you're seeing is likely just some mineral deposits that, as mentioned, can be removed with vinegar or other food-safe solvent.