Logisim - Logisim is an educational tool for designing and simulating digital logic circuits.
KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
BOOLR - Open-source digital logic simulator
Fritzing - Fritzing is an open-source initiative to support designers, artists, researchers and hobbyists to...
Logicly - - Design circuits quickly and easily with a modern and intuitive user interface with drag-and-drop...
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.