As pointed out earlier, Thomas S. Dye has converted the Org-manual to Org.
It's out of date, but may still be illustrative.
https://raw.githubusercontent.com/tsdye/orgmanual/master/orgmanual.org
> I could consider Org mode as a way of formatting manuals if I saw
> documentation presenting Org mode _as_ a way to format manuals.
> However, it would still have two big drawbacks as a candidate for GNU
> documentation.
>
> * It is a program. What we need is a format.
This claim is simply wrong.
(info "(org) Org syntax")
and
http://orgmode.org/worg/dev/org-syntax.html