Guest (above), have you tried my program HARMONY? I think it does a reasonable job of adding fairly simple chords (including to modal tunes). But it doesn't attempt the more complex chords with added 7th, 9th, 11th or 13ths - these are usually dependent on the style of the song (Jazz, Folk, Classical etc).

Nor does it attempt harmonisation in the strict technical sense.
I posted a link earlier.

I am not familiar with Chordie.