The official Kali documentation is split into small sections and covers most of the topics you’re likely to bbe interested in, ranging from installing Kali to more advanced topics such as installing Docker in the distro. Kali offers an official training course that features a certificate on completion. There is a separate page with summaries of the included security tools with links to their respective pages.
We didn’t think that anything would beat the Kali documentation, but the Parrot Security website takes a similar approach in terms of splitting the docs up into small articles, but there seem to be slightly more articles and they tend to be a little longer.
On the Pentoo website, clicking on the Docs link leads to a page with a small amount of information about boot options and a nine-year-old YouTube video about the project. There is also a brief FAQ. The documentation is underwhelming and it’s obvious that the developers expect the user to rely on Gentoo documentation and forums.
The BlackArch Linux site has a manual in PDF format. It covers installation, but much of the rest of the manual is effectively empty as it just says “Coming soon…”. The site does have a long list of all included tools with descriptions and links to the developer websites, though.
The BackBox site was something of a mess in this regard. The documentation link threw up a broken wiki link – a Telegram post seemed to indicate the wiki is defunct. Unless finding your way to the documentation is some weird metatest that we failed, getting it fixed would be our advice.