Polymer - New Google's UI Framework built on top of Web Components
With Polymer, Google has taken a new approach in moving the web forward.
From the website: "Polymer is a new type of library for the web, built on top of Web Components, and designed to leverage the evolving web platform on modern browsers."
For anyone who is familiar with Angular's Directives, Polymer will feel the same - it aims to bridge the gap between the future of ECMA script with Shadow Dom's and Web Components to modren browsers that have not implemented this feature yet.
Take a note for this one as a toolbox (the same as jquery) for spreading the reusable UI web components regardless the framework you use (angularjs, backbone, ember etc..).