See also:

https://infrequently.org/2015/06/progressive-apps-escaping-tabs-without-losing-our-soul/

http://www.pocketjavascript.com/blog/2015/11/23/introducing-pokedex-org

http://html5doctor.com/web-manifest-specification/

At their simplest, Progressive Web Apps are application-like things hosted on your web server. If you’re as old as me, you might call them “web sites”. They also point to a manifest file, which gives some light metadata about icons, default orientation and the like. In conforming browsers (currently, Opera for Android, Chrome for Android and, forthcoming, Firefox too) you can “save” the app to your homescreen. The relevant icon from the manifest is placed on the device’s homescreen which can then be tickled into life with your digit, indistinguishably from a native app: over HTTPS, if you so define it in the manifest, it can open in a default orientation and with no browser UI; with Service Worker, it can work offline.

In a nutshell:

Web sites(/apps) are getting more and more like native applications. Once this is implemented in a majority of browsers and operating systems, the main thing to figure out will be the UX that will make it feel natural (especially using "websites" offline). Check out pokedex.org - it feels smoother and more native in chrome on android than a lot of actual native android apps!

Between this, distributed websites, and webassembly, there's a lot to be excited about for the web to come!