KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Digital - A simulator for digital circuits.
Fritzing - Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to...
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.
BOOLR - Open-source digital logic simulator
Autodesk EAGLE - Autodesk EAGLE is an electronic design automation (EDA) software.