LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
FreeCAD - An open-source parametric 3D modeler
QCAD - QCAD is an application for computer aided drafting in 2D.
SketchUp - 3D for Everyone
nanoCAD - nanoCAD is a pro-grade 2D CAD system with native DWG support and full customizability.
Autodesk AutoCAD - Autodesk AutoCAD is a commercial computer-aided design (CAD) and drafting software application.