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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."
 
So how can I open .exe files on my Mac?

If you have an Intel-based Mac, install Windows on it. If you have a PowerPC-based Mac, you're out of luck. EXE files are Windows executables.
 
To be slightly more specific - a .exe file is a Windows-specific executable file. They require the Windows API to run. Since Mac OS X does not include the Windows API, they cannot be run on OS X. Hence why you need to install Windows (via Virtual PC for PowerPC Macs or Parallels/VMWare on Intel Macs) to run them.
 
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