I've been poking at this for 4 or 5 years now. It started as a simple simplified air pressure simulator for teaching logic programming. But now you can make all sorts of stuff with it, like logic gates, adders and I'm working on a replica 4004. (Links below)

The website is awful for new users - It doesn't work on mobile, there's no tutorial and no real documentation on how to use the editor. Instead of fixing that I'm working on making a dedicated puzzle game built around the engine to teach all the concepts up to and including getting players to build their own CPUs.

The backend is powered by a FRP compiler, which I'm really happy with. You can have huge steam powered worlds and incrementally edit parts of them, and it does fancy incremental recompilation.

Logic gates: https://steam.dance/nornagon/logic

2 full adders: https://steam.dance/josephg/adder

Miniaturised 8 bit ALU: https://steam.dance/josephg/alu

Work in progress CPU: https://steam.dance/josephg/4004_4