Theory pages
Disclaimer: The best source on the internet or the WORLD right now for music theory is Xenharmonic wiki, and the tuning list. If you really want to learn this in-depth, start here http://xenharmonic.wikispaces.com/Octave-based Equal Temperament Theory Pages (more soon)
16-tone - Allows for Cynder, Lemba, Magic, Mavila/Pelogic, and of course Diminished. key Designs have been made by Erv Wilson, Augusto Novarro, and organizations like Armodue.
Non-Octave Equal Temperaments
13-tone Bohlen-Pierce - Like the 12-tone scale which divides an 'Octave' (2/1 ratio) into 12 parts equally, this scale divides the 'Tritave' or "perfect 12th" (3/1 ratio, a fifth above the octave) into 13 equal parts. The result is a scale with harmony featuring odd-prime harmonics forming near perfect 3:5:7:9 justly tuned chords.
Just Intonation Tunings
Rod Poole's 17-tone 13-limit Just Intonation system - A proper page and description for this tuning will be here soon....