Hi, thanks for reaching out. Are you running the latest OS for Mac? The Steam version uses the same file so that won't help. I'll look into this some more and will keep you informed if I can get you a version that you can open.
Aha. I'll ask a friend of mine who has a Mac to try out the file and see if it works. The Steam library only has a Windows version at this time, since Apple needs to test the product before they allow the game to be available. I hope I can get the Mac version on there for December though, so I'll be sure to message you a key.