AsciiDoc belongs to the family of lightweight markup languages, the most renowned of which is Markdown. AsciiDoc stands out from this group because it supports all the structural elements necessary for drafting articles, technical manuals, books, presentations and prose.

This includes, for example, admonitions, variables, the include statement, example blocks, footnotes, keyboard macro, equations and formular support (albeid only with asciidoctor and installed plugin iirc), automatic toc and header, description lists, actually usable tables, etc ...

In combination with Antora one can built the most awesome, versioned, and Dont-Repeat-Yourself but-also "Fully-Explain-without-just-Linking" documentation ever.

GitHub has built-in support for it, albeid not for it's include directive, though that can be dealt with by using CI to invoke asciidoctor-reducer or publishing a github page that has been rendered using the asciidoctor/antora renderer.

https://docs.checkmk.com/ uses Asciidoctor. Linus Torvalds once recommended Asciidoctor (1).