That's very strange, as when I download it myself, I have to two text files and a folder called CATACLYSM.app which contains everything needed (including the actual .app file). I suspect that this is a problem with the name that Unity gave to the folder when I made the build. I've renamed the folder to simply "CATACLYSM" and re-uploaded.
Thank you for letting me know though! I'm going to look into renting a MAC book from the library or something so I can try it out myself.