[billmcneale]

Microsoft introduced this in Windows in 1993, it's called COM and is still in (heavy) use today.

It basically powers all inter communication in Windows.

[vaxman]

Not really. COM/OLE is a different paradigm, their answer to an infamous vaporware called Taligent/OpenDoc that bankrupted many developers. Microsoft was sort of stuck with that security nightmare though

[billmcneale]

COM is exactly what OP was talking about.

Apps can expose endpoints that can be listed, and external processes can call these endpoints.

[int_19h]

"COM" by itself is a rather broad umbrella. What you're describing seems to be OLE Automation. That's the one that has type libraries (which you need for discoverability).

And then Active Scripting was supposed to be how you'd script those endpoints...