Create a Jigsaw App for all platforms and devices

I need someone to create an app that will run smoothly on PC and Mac, tablet, I-phone and android. Once installed, the app needs to enable users to choose to try one of my digital jigsaws, based on the artwork from my children's picture books, and which will act as promotional tools for further book sales. I will need to update the site regularly with new jigsaws of my picture book artwork; therefore, I (the administrator) will need to be able to create jigsaws from my own digital photos and have the app alert users , when they log on to play, and by email, that there is a new jigsaw availble FREE. I would also like users to be able to create THEIR own jigsaws from their personal photos. The app will need to contain links to my books for sale and to other free activities for children. I want to ensure that once the user installs the app, they do not continue to see warning messages that this app is about to make changes to their hard drive as it is an executable file. I don't want any user to even consider that the app might contain a virus/ trojan etc. My business relies on good will and word of mouth advertising, so I can't afford for them to doubt the safetyof the app in any way.