In addition to Scala (which is freeware) there is also Melodos at
http://www.melodos.com/index2.htm.
Pros and cons:
Scala Pro:
1) free
2) many scales created by others are available
3) Windows and Mac OS versions (Mac requires X11 and the Mac developers' SDK but both are free upon registration at Apple's site)
Scala con:
1) Scala requires some detailed knowledge on the concept of temperament in music.
2) Not intuitive for the non-microtonality-interested musician
3) Requires additional software (freeware) to be controlled
Melodos pro:
1) Easier than Scala to use and quite intuitive
2) Specifically tailored for Byzantine music
3) scales are already available
4) Can input your music and let the software play it back based on ANY scale (yes, even dissonant ones!)
cons:
1) ONLY IN THE GREEK LANGUAGE (!!!)
2) ONLY IN WINDOWS (!!!!!!)
3) NOT FREE (400 EURO for total package)
and no, you cannot find it on bittorrent
Whichever software you choose it is MORE ACCURATE to use the ORIGINAL FRACTIONS of the tonal intervals and NOT the rounded integers.
Dr. George Michalakis and Mr. Haris Symeonidis have written excellent tutorials for MELODOS (Michalakis has an English version).
Many people can help with Scala (Basil?)
NG