Polymer is a lightweight library that helps you take full advantage of Web Components.
With Web Components, you can create reusable custom elements that interoperate seamlessly with the browser’s built-in elements, or break your app up into right-sized components, making your code cleaner and less expensive to maintain.
Polymer sprinkles a bit of sugar over the standard Web Components APIs, making it easier for you to get great results.
Polymer App Toolbox helps you build and deliver cutting-edge Progressive Web Apps with minimal overhead and payload, by leveraging powerful web platform features like Web Components, Service Worker and HTTP/2.
The Toolbox provides a component-based architecture, responsive layouts, a modular router, localization support, turnkey support for local storage and offline caching, and efficient delivery of unbundled app resources. Adopt these features individually, or use them together to build a full-featured Progressive Web App.
Learn more on https://www.polymer-project.org/