You can't get the application to work on your iMac, because the compatibility list doesn't mention anything about the Mac compatibility. According to the official System Requirements, the software works on the following Windows versions: Windows XP, Vista, Windows 7 & Windows 8. To make it work on your iMac, install Wine Bottler and then you should be able to run a Windows app inside Mac without the need to install Windows OS. You can obtain a trial of the GroundsKeeper Pro from the official website.