I am very late to this discussion, but I have used the big brother to 'Melody Assistant' for decades. Melody Assistant lasted me several years before I wanted a few extra features and upgraded.

You can use Melody Assistant free for as long as you like (with some limitations on length of tune, I think) or buy a lifetime licence for $40 once you know it suits your needs.

It can import and export in ABC and MIDI and many other things, as well as produce reasonable scores.

All of the songs which I loaded onto Jon Freeman's folkinfo site, now hosted by Joe Offer, are driven by ABC which I created from Melody/Harmony Assistant.