I am a huuge fan of AsciiDoc. The syntax is very similar to MarkDown, making the source easily readable. However it has a lot of extra features for rendering and composing source files so can be used to build all sorts of documents. You can render the same source into HTML, PDF, DocBook, and even a man-page format. Plus the tooling is available on CLI and in our Java Gradle projects using AsciiDoctorJ.
The post-processing translation to PDF, EPUB ... can be very useful.
I will add it to the list.
Also, feel free to share a documentation project, in the case is public.
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