There's Emacs's Org Mode.

nothing computational in there

That's not true. Org has a subsystem called Babel that can run code in lots of different languages, and it's pretty easy to add support for new ones.

Org Babel is the computational bit

it's a shame that "Show org source" is broken, but thanks, I'm intrigued.

I don't think this is true either. I went to one of the pages, https://orgmode.org/worg/org-contrib/babel/intro.html, clicked "Sow org source" and it took me to https://orgmode.org/worg/org-contrib/babel/intro.org.html, which does very nicely show the Org mode source code.

It's only broken on the front page, which tries to take you to https://orgmode.org.html/ when it should go to https://orgmode.org/worg/org-contrib/babel/index.org.html

If you want to see examples, look at the tutorial:

https://orgmode.org/worg/org-contrib/babel/intro.html

As for the source of that page, look at the Worg Maintenance section at https://orgmode.org/worg/

I haven't edited them yet, but I believe Worg is mostly org files on a Git repository - so you can clone it and see the source of all articles there.

org-mode + emacs-jupyter https://github.com/nnicandro/emacs-jupyter#org-mode-source-b...

mkdocs + mkdocs-material + mknotebooks