STP Viewer - Free STP Viewer - free software that lets you view 3D STEP files (.stp, .step file format).
A360 VIEWER - Free online CAD Viewer
3D Viewer Online - 3D Viewer Online is a web service and works on computers, tablets and smartphones.
Autodesk DWG TrueView - Get a free DWG viewer to view, open, edit, and convert .dwg files, the native file format for AutoCAD files. DWG Trueview includes DWG TrueConvert.
Glovius - Extensible & customizable 3D viewer, for consumption of product design data.
Online CAD viewer - Free online CAD viewer. Visualize obj, .step, .stp, .igs, .iges and .stl files.