Just a shame one package doesn't include every one of these features.
It's be complicated for us to provide a deep comparisons with every single existing doc tool. I've never used mdBook myself.
Bookdown/rMarkdown/Knitr is best explained at https://rmarkdown.rstudio.com/articles_intro.html#knitr-for-... and the user docs are at https://bookdown.org/yihui/rmarkdown/r-code.html and https://bookdown.org/yihui/rmarkdown/language-engines.html.
I like being able to test that the code in my documentation is valid and runs, and to show the output without having to copy and paste it.
Hope htat's useful!
When I looked at Docusaurus I had the impression it would work very well for JavaScript projects where you could runt he code in-browser, but wasn't designed to document other language code?
You can display real production source code in code blocks in any language without having to copy-paste and it can stay in sync.
The live playground allows you to display js code blocks and print the result in the browser. I don't see how this could work with other languages.