Textual media (books, websites, newspapers), anything goes here! Probably even some twitter threads could fit under this prompt. I suspect there have been a lot of interesting mechanisms here, even disregarding the fancier hypertext stuff.
Against Method has an “Analytical Index”, which is basically a sketch of the main argument together with page numbers.
The Timeless Way of Building has a “Detailed Table Of Contents” and key points highlighted throughout the book in italics.
- This personal website’s about page has some pretty neat accordions for content.