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Progressive Web Apps (PWAs) are web applications that are regular web pages or websites, but can appear to the user like traditional applications or native mobile applications. The application type attempts to combine features offered by most modern browsers with the benefits of a mobile experience.
In 2015, designer Frances Berriman and Google Chrome engineer Alex Russell coined the term "progressive web apps"  to describe apps taking advantage of new features supported by modern browsers, including service workers and web app manifests, that let users upgrade web apps to progressive web applications in their native operating system (OS). According to Google Developers, these characteristics are:
Progressive web apps are an enhancement of existing web technology. As such, they do not require separate bundling or distribution. Publication of a progressive web app is as it would be for any other web page. As of April 2018, progressive web apps are supported by the Google Chrome, Mozilla Firefox and Safari browsers, but more browsers may support the features needed in the future.
The technical baseline criteria for a site to be considered a progressive web app by browsers were described by Russell in a follow-up post:
By setting and manipulating the metadata for the web manifest file, developers enable user agents to create seamless native-like mobile experiences through the progressive web app.
Native mobile apps deliver rich experiences and high performance, purchased at the expense of storage space, lack of real-time updates, and low search engine visibility. Traditional web apps suffer from the inverse set of factors: lack of a native compiled executable, along with dependence on unreliable and potentially slow web connectivity. Service workers are used in an attempt to give progressive web apps the best of both these worlds.
Technically, service workers provide a scriptable network proxy in the web browser to manage the web/HTTP requests programmatically. The service workers lie between the network and device to supply the content. They are capable of using the cache mechanisms efficiently and allow error-free behavior during offline periods.
Properties of service workers
Benefits of service workers
Some progressive web apps use an architectural approach called the App Shell Model. For rapid loading, service workers store the Basic User Interface or "shell" of the responsive web design web application. This shell provides an initial static frame, a layout or architecture into which content can be loaded progressively as well as dynamically, allowing users to engage with the app despite varying degrees of web connectivity. Technically, the shell is a code bundle stored locally in the browser cache of the mobile device.
Cost of a progressive web app
For an app publisher, the biggest advantage is the cost saving in terms of app development and maintenance. Average customer acquisition costs may be up to ten times smaller compared to those of native applications. 
This list includes progressive web apps together with their scores from Google Chromes' PWA audit powered by Lighthouse. The audit validates the aspects of a PWA, as specified by Google's baseline PWA Checklist and ranges from 0 (worst) to 100 (best).
|ReSTbasis||Web Starter Kit.||||100|
|The Air Horner||An Air horn.||||100|
|chromestatus||Chrome Platform Status||||100|
|Dev.Opera||Web features and implementations||||73|
|Bet Calculator||Online bet calculator||||91|
|Expense Manager||Example expense manager|||
|Firefox Platform Status||Roadmap for web platform features|||
|Flipkart Lite||Online shopping||||55|
|Guitar Tuner||Tune a guitar||||82|
|Kite OnAir network||Kite Network|||
|koolsol||solitaire card game||||100|
|Memory Game PWA||||91|
|Polymon by Polymer|||
|QR Code Scanner||Offline QR code scanner||||100|
|sv-ginger||WebGL Morph Demo||||91|
|Wave-PD1||Synthesizer with Web Audio API||||73|
|Web Bluetooth (Intel® Edison demo)||||100|
|Web NFC enabled shopping cart||||100|
The following apps are or were claimed to be PWAs but fail to register an obligatory service worker: