Large collection of manuals, handbooks etc. for Hewlett-Packard calculators. Found on a post on the MoHP forum https://www.hpmuseum.org/forum/thread-19886-post-176204.html#pid176204

So you've written a UNIX utility, library, or driver—or have started writing one—and you want to document your work in a manual. What happens next?
Practical UNIX Manuals: mdoc is a guide for writing portable and maintainable UNIX manuals (manpages) in the mdoc language.
Why mdoc? Formatters for the language are available by default on all modern UNIX installations and may be downloaded for non-UNIX systems. Furthermore, mdoc annotates content semantically, not presentationally, producing consistent manpages across systems. For an analysis of mdoc and competing formats, refer to Fixing on a Standard Language for UNIX Manuals, published in the USENIX magazine.
I also feature the History of UNIX Manpages http://manpages.bsd.lv/history.html , which chronicles the development of manpages from the 1960s to the present day.

Linux man pages