Blender - Blender is the open source, cross platform suite of tools for 3D creation.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
SketchUp - 3D for Everyone
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
AC3D - AC3D is a 3D software for games, virtual reality and flight simulation, scientific, medical and general data visualisation, rapid prototypes of 3D designs, 3D printing, Google Earth, X-Plane, Second Life and more.
QUCS - Qucs, briefly for Quite Universal Circuit Simulator, is an integrated circuit simulator which means you are able to setup a circuit with a graphical user interface (GUI) and simulate the large-signal, small-signal and noise behaviour of the circuit.