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