From 8.1 the NGClient can have 2 files in its media folder, you can let Servoy generate those files through the context menu on the media node.
The manifest.json file that describes the application to the browser it is a w3c spec: https://www.w3.org/TR/appmanifest/
For android you can find an example here: https://developers.google.com/web/updates/2014/11/Support-for-installable-web-apps-with-webapp-manifest-in-chrome-38-for-Android
This is a more generic file where you can include for the NGClient any tag you want to have in the <head> section of the index.hml file.
The example that we ship has the same stuff as the manifest file above, but Apple/iOS doesn't support the manifest yet but uses some special meta tags for this: https://developer.apple.com/library/ios/documentation/AppleApplications/Reference/SafariWebContent/ConfiguringWebApplications/ConfiguringWebApplications.html
as an example we generate this: