LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
Free DWG Viewer - Free Viewer for DWG, DXF, DWF View AutoCAD DWG/DWF/DXF files View & measure DWG, DXF, DWF
FreeCAD - An open-source parametric 3D modeler
de·caff Viewer - The de·caff Viewer version 3.
SketchUp - 3D for Everyone
DXF View - A lightning-fast drawing viewer enables you to view DXF and DWG™ files on Mac