What are some examples of great documentation?

Maybe not quite on topic but I think the Physically Based Rendering book which combined code and documentation in the literate programming style is excellent:
pbrt.org/

Mozilla Developer Network (MDN) has helped me immensely; they document JavaScript (in particular) at a level where it's a good reference. It's complete, yet it doesn't assume an overly high level of knowledge.

Always been a big fan of the Stripe Docs:
stripe.com/docs

Also the Laravel docs are pretty awesome, the search is really good too:
laravel.com/docs

Positive Examples:

• Material Design
• Mail Chimp's Pattern Library
• Google something + "Digital Ocean". e.g. "Deploy NodeJS DigitalOcean". You'll probably get a pretty good guide.

Negative Examples:

• MongoDB - ...where do I even start? Literally. Where?
• Mongoose - they eventually make sense, but only once you're already are familiar with how mongoose works...
• Bootstrap v3 - This is contentious, but even after years of using Bootstrap, I always have difficulty finding stuff in the docs. I can never remember what's in the "CSS" vs "Components" vs "JavaScript" tabs and the navigation sidebar is painful to use

Edit: Bootstrap v4's documentation fixes most of the problems in v3's.

I'd second stripe in that their docs pretty pleasurable to look at, although I would say they can be a bit lacking when it comes to documenting references (lots of "see account update docs for full object", which at times isn't totally accurate).

Golang probably has the best documentation I've ever seen - it's not much to look at, but you can go from never writing a line of go to understanding it at a pretty deep level without ever leaving the site. There are both interactive docs and a a book on best practices directly on the site.

I was recently really impressed by the AirTable API docs, which take stripe's "docs on the left, code on the right" paradigm to a new level by contextualizing the docs to an existing project (step one is to select your project, step two is browse the docs with all your table names and stuff filled in). As such, "writing" code that interfaces with the API is primarily copy pasta, which is pretty productive. Not sure if it would scale to a more abstract API but this approach is fantastic for tables.

Django's docs are great to work with, concise and available in many different languages.

Always been a big fan of the Algolia documentation : algolia.com/doc/

I'm a big fan of Parse's documentation. There is a good balance between narrative and working code examples. Additionally, the navigation is superb; you are never more than two clicks from any other section of the documentation for the entire platform.

OpenBSD man pages. PostgreSQL documentation. Illumos source code.

So many comments and nobody mentioned Qt?

Qt docs are rather detailed and very helpful.

Negative examples: MSDN (with the "DWORD dwFlags -- a dword containing flags" style of descriptions) and Boost - where each library has it's own unique style of documentation and usually lacks badly on EXPLAINING the usage of the library in the right way.

I will give only positive examples:
Material Design
Google Guice
Mockito

Apple has done an amazing job at thorough documentation of their iOS platform and all the related libraries and concepts. I easily rank them and PHP's official documentation as some of the best examples of how to document a platform/system.

Well, it's cool that people are sharing popular documentations. It's mostly a result of a lot of contributions from a lot of people or a dedicated team.

What about documentations of a small team about a small to medium sized project? Nobody? I gotta say I'm disappointed.

Well, I'm shamelessly going to share one of mines because I believe you don't come up with documentations almost as perfect as the ones shared here, you build upon them.

My project documentations are definitely not the best out here, we already have enough great recommendations here to satisfy this post so I thought it would be okay to be different at this point.

I believe you have to start somewhere and I recommend, for a small to medium project, to take example of the documentation of my project called Libft as an example:

github.com/r4meau/libft

It's hosted on Github as README file and extended in a Wiki. I'm open to any critic :)

Maybe the best examples I've seen are Go and Elixir.

In Elixir, you cam write the main documentation for a module, for each public function and... write examples that can be run as real tests! They are, indeed, called "doctest" elixir-lang.org/getting-started/mi...

Golang has an excellent documentation system: it lets you edit/run the code in examples.

I've mentioned documentation systems rather than specific projects docs. Well, sometimes is the doc system that incentivizes writing docs. That's why Elixir, Golang and many other technologies usually have good documentation.

My 2cents

I' m mantainer of a small project ( small like one ) and i find super hard keeping documentation ok. Infact i m not managing at all.

I m trying to document it at best, but is not easy, dedicating time is not enough, you have also to know how to write nice docs and introductions.

the projects is fabricjs.com