You must know Falstad's circuitjs simulator, and I've been using it for some weeks for analogue designs. It's not perfect, I have found quite a few quirks, but this is also a logic simulator, not a highly powerful but capable and interactive one !
It took little time to draw the schematic of the INC8 unit and now I wonder why I wasted so much time doing it with Dia when I could also simulate the result and provide the source code (click here !)
With a few clicks I was even able to see where I made a mistake in the wiring.
I have stumbled upon a roadblock with the ALU8 and was feeling lazy to make a deep analysis of my mistakes, Falstad's circuitjs looks like the handy solution to that :-)
Now, is it possible to convert the netlist (extracted by my new tool) to display it with Falstad ? Or vice versa ?