But man pages are utterly useless if your question is
"what command do I need to use to do X?"
The permuted index is surprisingly useful in this regard but isn't always there in
manpage sources, you'd have to generate it. There are the technical memoranda too,
starting with V6 those were distributed with the manpages from what I know. Research and
BSD kept them packed in to the end but USG took them out starting with System V presumably
to make more paper documentation sales. The technical papers still hold a lot of value
imo and render much of the literature out there redundant. They're my preferred
source of "how do I do xyz" even if 1000 books have been published on the same
subject.
- Matt G.