Polymer lets you build encapsulated, reusable elements that work just like standard HTML elements, to use in building web applications. Developed by Polymer Authors
License: Open Source
Polymer is a powerful library focused on modern web standards and custom elements, making it ideal for building reusable, component-based applications. In contrast, KnockoutJS is a lightweight library that excels in data binding and the MVVM pattern, making it more suitable for simpler applications. Both have their strengths, but the choice between them largely depends on the complexity and requirements of the project.