xensynth
http://archive.org/details/xensynth
has abstractioins [ntof] and [ntof~]
which are not bound to the midi 100 cent interval
intervals can be set with a list message in frequency ratio format
xensynth can load scala .scl tuning files and when a .scl file is
loaded it sends the interval list to all the ntof and ntof interval
arrays.
ntof was based on xtof  , memory of original xtof library name escapes me at the moment.
i do remember the xtof version i had didnt work with non octave tunings so
i rewrote the patch to work with non octave tunings and added the audio rate version
seems like the differences in the control and audio versions might have been
[mod] and [%~] or % in an expr~