When Windows 8 shipped, Microsoft quietly shipped support for what they called a Hosted Web App (HWA). These are websites that reference a valid web manifest file and are served via HTTPS.
HWAs were an early precursor to progressive web apps. The obvious difference is no service worker requirement, which you would expect since the concept of a service worker had not be created yet.
To be a HWA, you would create a .appx file for your application containing the manifest file and a reference to the public URL. Then, you would submit the HWA appx to the Windows Store and consumers could install the HWA from the store.
The advantage of being a HWA is that these web apps have full access to all the Windows platform APIs, just like any native application. The reason that they have this privilege is that once installed, they form the store and are...