FreeCAD - An open-source parametric 3D modeler
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
QCAD - QCAD is an application for computer aided drafting in 2D.
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.