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