the download has a "zipx" extension.
I did a little googling and it looks like that is winzips new default compression method, and the only way to open the archive is with winzip, bitzipper, pkzip, or a couple of others. none of the compression utilities I typically use (7zip on Windows, unarchiver on mac) seem to support it.
Edit: sorry if I sound unappreciative, I just think its funny to use a proprietary closed format for distribution of software that is all about open software and formats. I'm currently trying to find something that will open this on the mac without being a scummy trial, or ill just do it on a pc.