Onshape - Onshape is the first full-cloud 3D CAD system. It runs in a web browser and on any mobile device.
A360 VIEWER - Free online CAD Viewer
DraftSight - Discover Dassault Systèmes®' DRAFTSIGHT™ Professional CAD software that lets you create, edit, view and markup any kind of 2D drawing. Learn more here.
STP Viewer - Free STP Viewer - free software that lets you view 3D STEP files (.stp, .step file format).
FreeCAD - An open-source parametric 3D modeler
Glovius - Extensible & customizable 3D viewer, for consumption of product design data.