Hi ohnowj,
We're sorry to hear that! We believe that, for some reason, certain types of Mac don't recognize the game as an application. This may happen when using non-standard unzipping programs that don't flag applications properly. Try opening the program with the default Unarchiver, and if that doesn't work, you can manually set the file permissions withchmod +x Fraction8\ Mac.app/Contents/MacOS/*in the command line. (We're not 100% certain of that syntax, so you may have to mess with it a bit.)
Apologies for the inconvenience!