LoCAD

LoCAD is a software for designing and simulating digital circuits.
Special emphasis is given to simple creation and graphical visualization of a circuit's functioning.

The inputs and outputs of the elements can be wired quite simply.
Usually, two touches are sufficient. The system searches a convenient way by itself.

In the simulation, you can watch the current flow and thus follow the cycle of state changes.
This way, your understanding of a circuit's functioning is enhanced, and your perception of circuit faults is improved.

It is possible to produce your own elements (ICs) with discretionary levels of nesting.
Like this, you can build big and complex circuits in a clearly arranged way. During the simulation, you can watch the state changes in all ICs.

A detailed introduction facilitates your familiarisation with the software.