Exported assets are free to use commercially and modify.

SSAOShader.js

SSAOShader

Screen-space occlusion

SSAOShader
Preview requires WebGL2. You can still download the demo.
Drag to orbit · Middle-drag to pan · Scroll to zoomOne finger to orbit · Two fingers to pan or zoom

Adds shadows where objects are close together, using only what the camera can see.

Official source