Progressive Web Apps (PWAs) provide an app-like user experience on the web by making use of modern web capabilities. PWAs use a web app manifest and service workers to work offline, receive push notifications, and load quickly. The web app manifest allows developers to define how the app should appear to users, while service workers cache assets to provide an app-shell experience regardless of network availability. Tools like sw-precache and sw-toolbox help generate service worker code and implement common caching strategies. By following best practices for manifests, service workers, and other features, web apps can achieve many of the benefits of native mobile apps without needing to be installed from an app store.