Easy Rider, From, the information I have seen in this thread and in the links provided from it, the piano WAS tuned in well temperament but this is no longer the case (JZG has mentioned that the change took equal temperament took place around 150 years ago) although I can see no reason why a piano could not be tuned that way.

The situation with a guitar (or any fretted instrument) must be a little different as you have the spacing of the frets to consider together with the number of strings running across these frets. My guess is that you would probably need staggered frets to make some tunings possible.

Jon