## TL;DR

PWAs are web applications that use modern APIs to deliver app-like experiences: installable (manifest.json), offline-capable (Service Workers), push notifications, and background sync. PWAs work across platforms from a single codebase.

## Core Explanation

Requirements: HTTPS, Web App Manifest (name, icons, start_url, display: standalone), registered Service Worker with fetch handler. App shell architecture: cache shell (UI), fetch content dynamically. Workbox (Google) simplifies Service Worker management. PWAs can be distributed via app stores (Trusted Web Activity on Android).

## Further Reading

- [Progressive Web Apps (MDN)](https://developer.mozilla.org/en-US/docs/Web/Progressive_web_apps)