On this website, I have urged players to be satisfied and happy with equal temperament (after an instrument has been truly compensated, and plays in tune). Accurate equal temperament allows guitar players to play in good tune, even when playing with other instruments, changing to any key, Using any open or closed chord forms, without re-tuning!
Nevertheless, with slight string bending, accomplished players, especially on electric guitars, can "sweeten" individual notes and chords to natural harmonies in real time, while they are playing.
Many would like to know more about temperaments - and why we don’t use a different scale, so as to produce natural harmonies. (A natural harmony occurs when the frequencies of two notes have a whole number ratio. For example, a note with a frequency of 1/2 of the other (an octave lower), or a note with a frequency of 1/3, 1/4, or 2/5 of the other. Overtones are natural harmonies of the root.)
This stuff is certainly not new! It goes back to Pythagoras, in the 6th century BC, and to the renaissance period, the 14th-17th centuries! Fortunately, there is much excellent information on the subject, so I will simply point you in the right direction. Please enjoy these links:
A Just Temperament Guitar Keyboard Rock on!
True Temperament is not a temperament; it’s a Company that builds guitar replacement necks and fretboards with wiggly shaped frets. Necks start at $795 – that’s unfinished and uninstalled. The frets are curved, with all notes placed according to experimental data. Most of their necks and guitars are set up to play in well temperament. You can select between two versions depending on what keys you prefer to play in.
They also build an equal temperament neck, again with notes placed according to experimental data. Starting with a straight nut, they shape the frets so that all notes are in correct locations, said to result in perfect pitch.
It’s very interesting to me that, when I look at the photo of the equal temperament neck, I can imagine that, with full compensation at the nut and saddle, those waves would mostly (but not entirely) go away!
Go to their FAQ Page for a good understanding of the products and principles.