If you download this and want to unpack this bizarre archive format on OS X: port install p7zip and then 7za e [filename].zip
It only took a few minutes to figure this out but if you're as confused by this quirky archive format as I was, there you go :) Don't bother trying to unpack the ZIP file in the normal OS X way as it'll just keep unpacking over and over and not give you anything useful.
It's one of the first things I install on any OS X system. Great unarchiver that takes care of most (all?) the common archive formats, although I run into the occasional password issue. It beats StuffIt without a doubt.
It only took a few minutes to figure this out but if you're as confused by this quirky archive format as I was, there you go :) Don't bother trying to unpack the ZIP file in the normal OS X way as it'll just keep unpacking over and over and not give you anything useful.