[TUHS] Is there a good, even definitive, list of reimplementations of the Unix kernel? What would good cut-off criteria be?

[Paul Winalski via TUHS]

On Sun, Apr 19, 2026 at 11:04 AM John Cowan <cowan at ccil.org> wrote:

> Solaris/Illumos, the major BSDs, QNX, BeOS/Haiku, IBM TPF, Stratus
> VOS, RISC OS, and Fuchsia are all Posix (at least), are still
> maintained, and have adopted ELF.  PE is used by Windows and its clone
> React/OS, the Mono framework for the CL, and UEFI.  Mach-O is used by
> iOS as well as macOS.
>

Thanks.  I had to implement Windows direct object file generation in a
compiler back end.  We already had COFF support for Unix.  My first idea
was to use conditional code to handle the Windows-specific features, but I
soon found that PECOFF was sufficiently different from Unix COFF that to
avoid an unmaintainable mess of conditionalization I ended up putting
PECOFF support in its own module.  PECOFF is a classic case of Microsoft's
adopt-then-extend philosophy.

-Paul W.