STEP (Standard for the Exchange of Product model data)
Its official name is ISO 10303 Industrial automation systems and integration -- Product data representation and exchange.
It is a open standard file format that was developed to enable data exchange between different CAD/CAM/CAE systems.
STEP files use the .stp or .step file extension.
They can represent 3D object geometry as well as non-geometric metadata like materials, textures, product manufacturing information (PMI) and more.
STEP is widely used in mechanical design, aerospace, automotive and other manufacturing industries to exchange product data between different software applications.
It is capable of representing very complex 3D data and models compared to simpler formats like STL.
Web Libraries for STEP
Three.js (javascript)
X3DOM (javascript/WebGL)
JSC3D (javascript)