A-Frame is a web framework, based on ThreeJS, for building virtual reality experiences. Make WebVR with HTML and Entity-Component. Works on Vive, Rift, Daydream, GearVR, desktop.
Three.js is a 3D library that tries to make it as easy as possible to get 3D content on a webpage. Three.js uses WebGL to draw 3D.It handles stuff like scenes, lights, shadows, materials, textures, 3d math, etc.