https://reference.wolfram.com/language/
It's detailed, complete, shows many examples for commom use cases, 'neat' examples showing what's possible, and lists down possible issues. I do see certain documentation quality issues sometimes.
The documentation itself is done using the features of Wolfram Language, so the examples can be run inline (depending on the platform).
1. Individual pages for each function.
2. Clear examples for common usecases.
3. Explicit documentation for input and return types.
4. The quick search is amazing - it prioritizes library reference over other pages.
5. Clean and useful references to related methods.
The user submitted notes were a big positive a decade ago - they highlighted common gotchas, workarounds, and surprising alternatives, but have gotten dated over time (kinda like SO answers). But the voting mechanism attempts to keep them in check.
Compare https://www.php.net/manual/en/function.str-contains.php to the tiny one paragram you get at https://docs.python.org/3/library/stdtypes.html#str.find (which then redirects most users to a far more confusing explanation about the in operator https://docs.python.org/3/reference/expressions.html#members...
I usually prefer to read their docs rather than the ones in man pages which are "flat" (all the initiation had the same importance)
There are three main files:
Starter Guide: https://docs.haproxy.org/3.0/intro.html
Configuration Manual: https://docs.haproxy.org/3.0/configuration.html
Management Guide: https://docs.haproxy.org/3.0/management.html
Having all the similar docs together in the same file (all config options, for example) is refreshingly simple.
I see answers here that are oriented towards completely different parts.
For open source projects, Django [2] is pretty close to the gold standard.
[1] https://help.hcl-software.com/dom_designer/14.0.0/index.html
In general, I like how it is easy to access any kind of information about Emacs (keybindings, commands, variable values, active modes, text/face styles, etc.) from anywhere within Emacs through the C-h shortcuts or via “Help” in the menubar. Contrast that with what is usually offered as “Help” in most other applications and how hard it is to find just some basic piece of information.
I personally love the Documentation for Kirby CMS:
https://getkirby.com/docs/guide
For a project: MDN, they refactored the Web's JS documentation
Stripe
Django
Hubspot
Mercurial with comments https://hgbook.red-bean.com/read/a-tour-of-mercurial-the-bas...
This in turn means that the structure and style is shared by many libs in the ecosystem, and everything is natively cross-referenced.
Documentation facilities in Elixir are extremely powerful, as you can use Elixir to generate the documentation itself! See e.g. the way UML diagrams are embedded here: https://hexdocs.pm/say_cheez_ex/readme.html#uml-dot-graphs - nothing stops you from creating them dynamically based on external information, test results, external services or whatnot.
https://www.buildbuddy.io/docs/introduction/
I don't think I ever had a case that wasn't covered in the docs.