theme-color Meta Tag
Meta tag to define a suggested color that browsers should use to customize the display of the page or of the surrounding user interface. The meta tag overrides any theme-color set in the web app manifest.
Offline web applications
Now deprecated method of defining web page files to be cached using a cache manifest file, allowing them to work offline on subsequent visits to the page.
Add to home screen (A2HS)
The ability for a user to "install" a website and use it as if it was a natively installed app. To enable this behaviour, a website must serve a valid Web App Manifest and load it's assets through a [Service Worker](https://caniuse.com/#feat=serviceworkers).