Listener asked last time about how to document a large system with databases, microservices, and more without documentation. A few tools for documenting individual languages were mentioned, and as mentioned, this is good for the API documentation, but doesn't really help give someone the big picture.

One idea is a mind map tool (like Freeplane). This can provide a free-form way to show at a high level how all the parts link together, and attach as much details as needed (like credentials or links to generated API documentation, etc.).