Zix is a scam. It's a fake compression protocol that doesn't actually compress anything. It just places the file in a wrapper that requires WinZix (which comes loaded with adware and spyware) to open. Far and away the most common place you'll find .zix files is in illegal torrents, usually seeded by the folks who are trying to infect computers with adware with their program.
Since OS X doesn't have adware/spyware they probably don't have any interest in making a Mac version of their "product."