[dom0]

Nowadays Sphinx is quite usable for writing both long-form documentation and reference docs.

It's a really complex piece of software (much more complex than everyone thinks at first), but most of the time that isn't noticeable. The rST syntax can be somewhat confusing with advanced constructs, but for most stuff a short primer gets everyone going in the right direction. Since it's Python, deployment is a little bit annoying on non-Linux machines, but for docs you want CI anyway. To tweak PDF (i.e. latex) output it requires a fair bit of knowledge of both Sphinx and latex (and possibly rST [0]).

Like I said... it's quite usable.

[0] rST again being much more complex than everyone thinks at first. It's an enterprise markup language.