KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
FreeCAD - An open-source parametric 3D modeler
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
SketchUp - 3D for Everyone
EasyEDA - EasyEDA - Web-based EDA suite; runs in browser.
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.