FreeCAD - An open-source parametric 3D modeler
Fritzing - Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to...
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.
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
QCAD - QCAD is an application for computer aided drafting in 2D.
LTspice - LTspice® is a high performance SPICE simulation software, schematic capture and waveform viewer with enhancements and models for easing the simulation of analog circuits.