Downloaded Prezi Not Working on Mac OS X 10.6.8

I recently downloaded my Prezi on Fun with an American Grandmother and the .exe file works on a PC, but there is not red icon on my Mac. In the past, downloaded Prezis worked fine, but now they don't work on my iMac or MacBookPro. I tried downloading it multiple times, but to no effect. Please help!

Thanks,

Greg Brooks-English