Preact is an attempt to recreate the core value proposition of React (or similar libraries like Mithril) using as little code as possible, with first-class support for ES2015. Currently the library is around 3kb (minified & gzipped).

It retains a large amount of compatibility with React, but only the stateless functional components and ES6 Classes interfaces. As one would expect coming from React, Components are simple building blocks for composing a User Interface. - PreactJS.com