FreeCAD - An open-source parametric 3D modeler
OpenSCAD - OpenSCAD is a software for creating solid 3D CAD objects.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
T-FLEX CAD - Top Systems offers the comprehensive set of integrated applications for T-FLEX Parametric CAD, including CAM, FEA and PDM
QCAD - QCAD is an application for computer aided drafting in 2D.