A page I use each day every day. Fantastic way to centrally search through everything quickly.
The only downside is that some doc updates make your existing configuration unreadable, so you have to re-select which documentations you had enabled.
Nice website. There is also Zeal: https://zealdocs.org/ and for other type of documents. There is Kiwix: https://kiwix.org , which I use to download the entire Wikipedia.
I was never able to have truly offline / portability with zeal, if you move to another computer it seems to lose all docs.
You can just transfer the files and it should find them again. I did that with Kiwix and Zeal, if I’m not mistaken. Nowadays I don’t use Zeal, but don’t remember having such a trouble when installing a new os and taking old HDD over.