LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
OpenSCAD - OpenSCAD is a software for creating solid 3D CAD objects.
QCAD - QCAD is an application for computer aided drafting in 2D.
FreeCAD - An open-source parametric 3D modeler
SketchUp Make - SketchUp Make is a best in the class CAD software capable of performing 2D and 3D rendering and designing, however, best for the 2D projects.
T-FLEX CAD - Top Systems offers the comprehensive set of integrated applications for T-FLEX Parametric CAD, including CAM, FEA and PDM