The ketoplans Progressive Web App (PWA) can be installed with the Add to Home screen (A2HS) button. A2HS is a feature available in modern browsers that allows a user to install a web app, ie. add a shortcut to their Home screen representing their favorite web app (or site) so they can subsequently access it with a single tap.
The Progressive Web App philosophy aims to give web apps the same user experience advantages as native apps but can also be seamlessly cross-platform and updated in real-time. Part of this is the simple gesture of accessing an app by tapping its icon on your Home screen, and then having it appear neatly in its own window. A2HS is supported in all mobile browsers and also in some Chromium desktop browsers.
The more you use the PWA the more information it will store on your device and this will allow you to use the app even when you are offline.