Preact.js - Preact is a fast 3kB alternative to React with the same modern API. Components & Virtual DOM.
Inferno - An extremely fast React-like javascript library for building modern user interfaces.
Glimmer - Fast and light-weight UI components for the web
w2ui - W2UI is a small JavaScript UI library with a complete set of widgets: layout, grid, sidebar, toolbar, tabs, fields, popup, utilities.
CanJS - CanJS is a JavaScript library that makes developing complex applications simple and fast.
Svelte - Cybernetically enhanced web apps