The Consonant Keyboard

The consonant keyboard is an instrument that allows you to incorporate more pure, justly-tuned intervals into standard equal temperament. This patch maps intervals on a standard midi keyboard to user-defined ratios and gets the frequency of new notes by multiplying existing notes by those ratios. It uses an advanced and highly customizable algorithm to do this, you can exclusively use just intonation or equal temperament depending on the settings, but under the default settings it blends the two.

for more info on just intonation see
-http://en.wikipedia.org/wiki/Just_intonation
-http://www.kylegann.com/tuning.html