LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
SketchUp - 3D for Everyone
QCAD - QCAD is an application for computer aided drafting in 2D.
TYCAD - TYCAD is a application for computer aided drafting (CAD) in two dimensions (2D).
FreeCAD - An open-source parametric 3D modeler
JustCAD - JustCad is designed, to make cad drawing as simple as possible.