Are the offline versions powered by HTML5 also?

The offline standalone versions for Mac and Windows do actually utilize Flash. The Flash Player comes included/contained with the offline executable/application file so there is no need for the end-reader to have Flash installed already – the required Flash Player is packaged with the offline file. Using Flash in this instance is not a problem since the offline magazine runs outside of any web browsers and instead runs natively on the machine. The offline versions for iOS and Android are app based. The free Flipbook Viewer app for iOS and Android can essentially download the online flipbook content for offline viewing. These are optional features.