Previous feedback seemed to indicate that the tool wasn't operating anymore under later versions of OSX. However, as of this writing, I can report the tool still works just fine under OSX 10.5.8 with two caveats:

1. You must draganddrop your par2 file onto the app-icon, the menu's are indeed greyed out, as mentioned before.
2. The par2formac must be on a path without spaces or other special characters in the name. It seems to use an unquoted reference to itself and this breaks when your path has spaces, or possibly other special characters.

Problems such as what I mentioned for the second caveat are reported when the app opens, just read the dialog carefully :) I agree, the interface is crude, but hey, the tool works! It just saved me from having to wait for the last 4 Gig of a huge database dowload!