I would place the Windows Internals book series on that list, BeOS, Mac OS books from Apple (pre-OS X ones), Plan 9 books, Programming Inferno, for example.
Bitsavers has a lot of stuff http://bitsavers.org/pdf/
And 1000 bit has lots of brochures and old technical magazines.
It's not about any OS in particular, but Per Brinch Hansen has a book called Classic Operating Systems: From Batch Processing To Distributed Systems, which showcases a lot of historically important essays in operating system history. The back of the book says it "includes a bibliography of about 60 operating systems".
You can borrow it on archive.org: https://archive.org/details/isbn_9780387951133/mode/1up
I'd like to see a non-Unix "alternative OS classics" list to supplement the Unix list.
Maybe a non-TCP/IP/Ethernet "alternative network classics" list as well.
Since these are mostly vintage (though nice reads) I'd also like to see a list of "modern (or future) systems classics" as well.