Three.js - This popular library is a great way to create 3D animations on the browser, using WebGL in an intuitive way. Providing canvas, svg, CSS3D and WebGL renderers, this library lets us create rich interactive experiences across devices and browsers.
Mo.js - This library is a motion graphics toolbelt for the web, with simple declarative APIs, cross-device compatibility and over 1500 unit-tests. Tutorial
Popmotion - Popmotion allows developers to create animations and interactions from actions, which are streams of values that can be started and stopped, and created with CSS, SVG, React, three.js and any API that accepts a number as an input.
Scroll Reveal - This library provides easy scroll animations for web and mobile browsers, to reveal things on-scroll in an animated way.