FreeCAD - An open-source parametric 3D modeler
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
OpenSCAD - OpenSCAD is a software for creating solid 3D CAD objects.
Fritzing - Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to...
LibreCAD - An open source 2D CAD application for Windows, Apple and Linux.
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.