I noticed that you put Guitar Pro and Power Tab, but not Tux Guitar. Tux is a great fretting program and its all free, and it also exports the same way. (File>Export>Midi) So if you want to add it to your tab readers, here is the link. http://www.tuxguitar.com.ar/
I was also wondering if there were any other programs for fretting that are available to Mac, as that is the only computer I own.
Does Tux open GP and Ptabs? I don't know anything about mac... Anvil Studio is a similar one... maybe they have mac support!?