You will laugh, but Apple started to call “cross platform” things that are used or run on more than one of their product. So cross platform between iOS, macOS, Apple TV OS(?), watchOS.

Technically correct, the best type of correct (for a marketing team).

Microsoft does that too. It's infuriating.

But all of those run Darwin, so for something like a graphics API that has nothing to do with GUIs and whatnot, the "platform" for all of those is the same.

Says someone that never read Apple documentation or iDevice literature regarding system programming on Apple platforms.

You can start by reading the Mac OS X Internals, followed by Mac OS X and iOS Internals: To the Apple's Core.

Then hop over to Apple's archive, https://developer.apple.com/library/archive/navigation/

Fair enough :)

It is "cross-platform" in the same way Direct3D is.

In this vein and previously discussed on HN[1], but there is a weird DX3D bridge in Linux that is available on WSL2. Still not "cross-platform" and seems to mostly exist to support ML workloads for Windows users.

1] https://news.ycombinator.com/item?id=23241040

You are completely right, I shouldn't have included that in the list above.