If I buy the Mac version can I download for free on my iPad/iPhone?

If you’d like to run the app on your Mac and iPad/iPhone, separate purchases are necessary. The reason for this is that each app runs on a different operating system — Mac on OSX and iPad/iPhone on iOS. Because of this, apps for each platform have to be developed from the ground up and are sold separately through their respective stores i.e. Mac App Store and App Store.