If you want to hear old tunings, listen to recent recording of harpsichord music or Baroque chamber music by players who know what they're doing. They will usually be in some kind of non-ET tuning and they'll say what that tuning is on the CD sleeve.

Here is a discussion of present-day orchestral pitch standards:

A=440 or A=442?

Folkies tend to prefer A-440 and most fixed-pitch folk instruments are tuned that way. (The exception being accordions owned by egomaniacal arseholes who like to be sharper than everybody else and stand out by being out of tune; they like A=443).

The first person to work out the correlation between frequency and pitch was Mersenne in the 1630s. I don't know exactly how he did it.

This seems like a reasonably sane treatment of the historical issues around temperament:

Pythagoras and the Wolf