I am not sure I personally consider that closely enough related to count.
It often seems to me that even today Amiga fans are so passionate about the machine that they make rather exaggerated claims that do not really stand up.
For instance in many places I have read the claim that AmigaOS was a microkernel OS, or closely-related claims such as that it was the first widespread microkernel, or the first GUI microkernel, and so on.
The point of a microkernel is that only the microkernel runs in kernel space (in x86 terms, in Ring 0) and the rest of the OS is divided into multiple "servers" which run in user space (again in x86 terms, in ring 2 to 3). This in turn brings a problem, which is how to make comms between the microkernel and the servers fast. IPC is the big problem and that is what microkernel OSes struggle with, which has shaped the design of Mach, XNU, L4, seL4 etc.
AmigaOS is small but everything runs in ring 0. There is no division and so there is no need for tricky performance-critical IPC and all processes can read and write each others' RAM. That makes it (1) easy (2) fast (3) not a microkernel.
I would regard direct blitting into 2D windows as not unique, not the first such implementation, and not the same as 3D compositing.
In AmigaOS, everything runs in unprivileged mode, except for some specific critical code within exec.library which runs in supervisor mode or interrupt mode.
What's true is that exec.library does offer a call to run code as supervisor[0], and that there's no memory protection.
FWIW I am also linking to AmigaOS 4, MorphOS and AROS...
I wish "Notch" Persson or some other billionaire nerd would just buy the things and declare the whole lot freeware. There surely cannot be much residual value to extract any more.
