The greatest source for music theory in the world.

http://xenharmonic.wikispaces.com 

http://xenharmonic.wikispaces.com/General+Theory

This was created some time ago now by Andrew Heathwaite and Jacob Barton, however many people have contributed to this encyclopedia of music-history, theory, math, philosophy, etc... One person whose efforts have been exhaustive and inspiring is Gene Ward Smith. Look at the updates on the wiki for a moment... o.O  

Some astonishingly clean pages have been created that sum up months of work of the Xenharmonic Alliance on facebook - thanks to Keenan Pepper and Mike Battaglia we have pages like:

http://xenharmonic.wikispaces.com/Mavila+Temperament+Modal+Harmony

These mavila modes in guitar scale-chart form can be found below in an earlier post. -RS

Favorite Microtonal Guitars of the Past......

16-tone steinberger

 16-tone 9-string hand build

 19-tone Ibanez RG

 21-tone RG

 23-tone 8-str RG neck build

 25-tone RG

16-tone RG

1/2 Octave period Tuning for 16-tone Guitar

Here is an example of how a scale like Lemba looks when tuning in tritones. It changes everything, and really makes it easier to play sequences, arpeggios and scales in Lemba or any 1/2 octave period scale. Once you adapt, you'll find writing and melody to be intuitively easy. This is set up for f# on top e string and c where b string typically falls on standard guitar (to give you an idea of the string gauges you'll need)..  On a 7-string 3 octave arpeggios are in one position, and you get a low F#........meaning more range than an 8-string on a 7-string!  B) 

16-tone Microtonal Guitar Theory / Scales / Mavila tuning

Here are some examples from the 16-tone equal temperament scale book, 'Hexadecaphonic Scales for Guitar'.