And now I feel like an idiot for posting this having read who you are

It does help the rest of us though. I'll also mention for the same reason that there was a thing called ReWire on Windows, not sure what became of it.

Rewire is fairly different. It still exists, and also existed for macOS too. But to use it, applications have to be explicitly coded to use it (and linked against the rewire SDK).

That's quite different from JACK, SoundFlower, Hijack and the innumerable other inter-application audio routing systems for macOS, which can be used without the applications knowing anything about them.

The functionally named but utterly undescriptive GraphEdit, which was at some point part of the DirectX SDK allowed you to build arbitrary pipelines (that normally you'd have to configure via code in your app) for input/output of multimedia data. I haven't done directX programming in over a decade though so I have no idea if it's comparable to ReWire, but GraphEdit was an unsung hero back when I was.

The DirectX SDK in this respect is like GStreamer on Linux: it allows an application to build arbitrarily complex pipelines for data processing. Emphasis on within the application.

However, it did not and does not provide for inter-application audio/MIDI routing, which is what tools like JACK, Rewire, SoundFlower, Audio Hijack and others are all about.