AcceliCAD - CAD program that's compatible with the .DWG file format and industry standard applications
SketchUp - 3D for Everyone
FreeCAD - An open-source parametric 3D modeler
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
CADian - 2D/3D CAD provides a high degree of compatibility with the AutoCAD command set, as well as AutoLISP...
DraftSight - Discover Dassault Systèmes®' DRAFTSIGHT™ Professional CAD software that lets you create, edit, view and markup any kind of 2D drawing. Learn more here.