What is AMiga OS 4.1 based on?

[Linde]

Yes of course, that's why I didn't say ALL source code... but now you are just pointlessly pointing out irrelevancies!

Oh ok.

According to the Friedens, very little of the original 3.1 source code was usable (search ann.lu for the quotes). Which would make sense given that it was all 68k asm.

all

[Linde]

One might expect a Windows clone to run software written for Windows -- or an AmigaOS clone to run software for ?   (just a harmless stab)

It tries to be a clone of the operating system, not the underlying hardware, which is also a requirement for binary level compatability with Amiga applications.