Gem.js!

HTML is great for declaring static documents, but it falters when we try to use it for declaring dynamic views in web-applications. AngularJS lets you extend HTML vocabulary for your application. The resulting environment is extraordinarily expressive, readable, and quick to develop.

Polymer is a library that uses the latest web technologies to let you create custom HTML elements. Build anything from a button to a complete application as an encapsulated, reusable element that works across desktop and mobile.

You can write less code with Ember's Handlebars integrated templates that update automatically when the underlying data changes.

Backbone supplies structure to JavaScript-heavy applications by providing models with key-value binding and custom events, collections with a rich API of enumerable functions, views with declarative event handling, and connects it all to your existing application over a RESTful JSON interface.

Knockout is a JavaScript library that helps you to create rich, responsive display and editor user interfaces with a clean underlying data model. Any time you have sections of UI that update dynamically (e.g., changing depending on the user’s actions or when an external data source changes), KO can help you implement it more simply and maintainably.

Ext JS is a JavaScript library for building interactive web applications using techniques such as Ajax, DHTML and DOM scripting. Ext includes interoperability with jQuery and Prototype.

Riot lets you build user interfaces with custom tags using simple and enjoyable syntax. It uses a virtual DOM similar to React but faster. Riot is very tiny compared to industry standards. We think there is a clear need for another UI library.

MWF works together as a series of page types, modules, and components. It’s a system that allows site authors to consider how best to tell the story of Microsoft products and services with confidence that the modular pieces will support and work together.

Marko is a modern, progressive UI library built and used by eBay for fast and friendly web development. It provides an elegant and readable syntax for both single-file components and components broken into separate files and includes a bunch of examples and an intuitive tool to try it out online.

Preact is a fast UI framework with the same same ES6 API as React but just 3kB in size. Virtual DOM Components and high React compatibility help with familiarity and re-usability.

Rax is a universal JavaScript library built and used by Alibaba.com that has a largely React compatible API.