Ok, technically it's "Pay What You Want" with a $0 minimum.
If you've done any mobile development, you probably know how painful it can be to deploy your apps to the App Store or Google Play. I found this out the hard way after I had Google reject one of my apps and Apple reject two of them. Apple rejected one simply because it had no useful content (ouch!).
When I learned that you can take just about any web application, add a little code and some meta data, and make it available on both desktop and mobile devices, I was ecstatic.
PWAs can be installed on any device and then they work just like a native app. They appear on your device's home screen, have custom icons and launch screens, and should also work offline. Done right, it's nearly impossible to tell a PWA from a mobile app.
Some of the more popular and successful PWAs include:
You can find more PWAs at https://progressivewebapp.store.
I'm currently working on a new game based on the "Spot It!" card game. Although it is not yet a PWA, it will be converted into one soon.
If you want to make your own PWA, you can download the book free. If you're feeling really generous, you're also welcome to pay something for it. I won't complain either way.