KiCad - A Cross Platform and Open Source Electronics Design Automation Suite
Logisim - Logisim is an educational tool for designing and simulating digital logic circuits.
EasyEDA - EasyEDA - Web-based EDA suite; runs in browser.
BOOLR - Open-source digital logic simulator
Proteus PCB design - Proteus PCB design combines the schematic capture and ARES PCB layout programs to provide a...
Digital - A simulator for digital circuits.