FreeCAD - An open-source parametric 3D modeler
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...
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
EasyEDA - EasyEDA - Web-based EDA suite; runs in browser.