JDigitalSimulator is a platform independent open source Electronic Design Automation software entirely written in Java. As JDigitalSimulator is open source, it comes absolutely free of any charge.
JDigitalSimulator has a wide range of build-in digital circuit elements, such as logic gates, flip-flops, switches, and displays. Drawing a circuit in JDigitalSimulator is as simple as using a paint program. Click the circuit element icon in the toolbar and drag it to the position where you want the element to go. Use a similar procedure to draw wires and indicate connections. It's that simple.