> MIT's PCC ports to various micros, especailly x86, also used b.out that
> was quite similar to a.out.
>

That was a cross-compiler, right? If so, I remember going over to MIT-LCS
and picking up a copy of the sources for the compiler and the MIT PC/IP
implementation. I had to show a copy of my ATT source license to the
secretary, who made a copy of a 9track tape for me.She was  a hoot: dressed
like a punk, and we takled about not working for defense companies. We were
then able to build and install various TCP/IP utilities on our PC-AT
machines running early Windows releases.  This was probably early 1980's. I
think the PC/IP code was based on David Clark's upcalls idea[1]. It later
became the basis for FTP software, which then died when Microsoft added TCP
to windows.

[1]
https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=e7c6da568d15a3ea50854dbd951c1d6394502a15