apropos
to search man pages, otherwise I use man
Free and Open Source Software
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
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Probably not quite what you're looking for, but you can download the ArchWiki https://archlinux.org/packages/extra/any/arch-wiki-docs/ https://github.com/lahwaacz/arch-wiki-docs
Maybe not exactly what you are looking for, but you could use a website archiving solution to store one of those online man-page collections. I know it sounds like overkill, but it's actually easy to setup and can be used for all kinds of other things as well. For instance, I have a local docker container running SOSSE for C++ and Python references and for all kind of libraries and APIs I use for software development. This way I have everything I need on my laptop and can work anywhere, even if there is no network connection.