SketchUp - 3D for Everyone
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
nanoCAD - nanoCAD is a pro-grade 2D CAD system with native DWG support and full customizability.
FreeCAD - An open-source parametric 3D modeler
BricsCAD - A powerful CAD platform, with features familiar to you from native .dwg applications.
Autodesk AutoCAD - Autodesk AutoCAD is a commercial computer-aided design (CAD) and drafting software application.