A few years ago, a popular application was a simple game called 2048. The goal is to combine blocks with numbers to ultimately total 2048. Blocks are numbered in multiples of 2. You can combine adjacent blocks with the same value to create a new block with their combined value.
I wasted more time playing this game than I care to admit. It is easy to play and highly addictive. A well-crafted brew of endorphins and gameplay.
Fortunately, there were numerous open source knock-offs available on GitHub. Several were web applications. I would wager that native versions distributed through app stores were websites wrapped in a native shell, a hybrid application.
I chose a popular repository to fork for the book. The 2048 web application is simple and a perfect candidate to demonstrate how to make an exemplary PWA example: