Three.js (https://github.com/mrdoob/three.js) is an open source library that powers many of the WebGL applications on the web. It aims to create an easy to use, lightweight, 3D library, with multiple renderers that target 2D canvas, WebGL, SVG, and CSS3D. Here's a neat demo of a rotating cube, showcasing the simplicity of the Three.js API:

let
  renderer,
  scene,
  camera,
  mesh,
  width = window.innerWidth,
  height = window.innerHeight;

function init() {
  camera = new THREE.PerspectiveCamera(70, width / height, 0.01, 10);
  camera.position.z = 1;

  scene = new THREE.Scene();

  const mesh = new THREE.Mesh(
    // geometry
    new THREE.BoxGeometry(0.2, 0.2, 0.2),
    // material
    new THREE.MeshNormalMaterial()
  );
  scene.add(mesh);

  renderer = new THREE.WebGLRenderer({ antialias: true });
  renderer.setSize(width, height);
  document.body.appendChild(renderer.domElement);
}

function render() {
  requestAnimationFrame(render);
  mesh.rotation.x += 0.01;
  mesh.rotation.y += 0.02;
  renderer.render(scene, camera);
}

init();
render();

You can see the live demo on their GitHub page, which resembles the following: