Glimmer - Fast and light-weight UI components for the web
Vue.js - Reactive Components for Modern Web Interfaces
Svelte - Cybernetically enhanced web apps
Webix UI - An enterprise JavaScript Library for cross-platform app development with HTML5 JavaScript widgets and easy integration with most popular JavaScript Frameworks.
Preact.js - Preact is a fast 3kB alternative to React with the same modern API. Components & Virtual DOM.
Polymer - Polymer is a library that uses the latest web technologies to let you create custom HTML elements.