You've probably heard of Unified Modeling Language (UML). You've probably even drawn up a few system diagrams with it. It's so popular that tools like Visio and Google Draw have the templates built in. But does it work? It's certainly good for analysing an existing system and understanding the relationships between the parts, but what about up-front design. Doing UML right often requires you to know, or make decisions about, things that aren't done yet. Things where there requirements aren't even done yet, let alone the detailed design.
That's where NoUML comes in. If UML is supposed to be an abstraction of your system, NoUML is an abstraction of that. It's even more simplified, and it focuses not on the components, but on the _relationships_ between them. Everything else is left as an implementation detail.
Even the possible relationships are limited. There are only 3 kinds of relationships:
and they're very generic. For example, "Is" doesn't imply any language inheritance. It's duck typing without any types. Similarly, "Has" doesn't imply contains, just an association. "Uses" is for the things something needs, but are associated in any other way. And of course there are rules for heritage and ownership, which helps break things down into discrete components.
But where NoUML shines is in how those discrete components relate to each other. They help you see where the transitive dependencies are and help keep you from turning those transitive dependencies into direct dependencies. It helps you keep your abstractions from leaking out into neighboring components. It keeps your bounded contexts bounded. And when you're building large scale distributed systems anything you can do to keep your boundaries clean and clear will pay big dividends. If not immediately, then soon.