For portability I usually just use Bootstrap (https://getbootstrap.com/) or template with a basic layout and fill it in with HandlebarsJS (https://handlebarsjs.com/) and jQuery. To compile apps I will use:

* Nativefier for desktop application to create a basic Electron application from a website (https://github.com/jiahaog/nativefier)

* Web2Executable to convert a local set of HTML and NodeJS to a NWJS binary file (https://github.com/jyapayne/Web2Executable) - FYI: NWJS, or NodeJS + Webkit and then Chrome rendering engine, is the code that Electron is based on. The big difference is that NWJS doesn't require all the structure that Electron does. So NWJS is easier to develop for but in some cases not as fast to execute.

* Appsgeyser.com (http://appsgeyser.com) can convert either a website or a zip file to an Android application

* GoNative.io (https://gonative.io/) will create apps for Android and iOS. But some of the advance features are stuck behind a paywall.