As best as I can tell, the standard name for these is 'scroll spy'. Gwern.nt mobile example: https://gwern.net/doc/design/2023-04-28-gwern-gwernnet-mobil...
They are becoming increasingly common as web browsers/OSes kill scroll bars and you are forced to implement your own: https://artemis.sh/2023/10/12/scrollbars.html
> I’ve seen this floating ToC done before, but could not find a site off the top of my head that implements the feature
Gwern.net has it! It's just that because we use both margins already, there is usually not enough horizontal space. But if you have a wide enough screen, you should see it, like https://gwern.net/doc/design/2023-08-07-gwern-gwernnet-deskt... You can also see this on LessWrong.com and https://80000hours.org/podcast/ podcasts.
> Relatively often I come across pages that have unique IDs for each header, but no clickable links! I end up having to use inspect element to find the anchor points.
Chrome has a 'link to text fragment' feature for this which got standardized and which Firefox is supposed to support at some point. So not so necessary as it used to be. (The unique IDs are often not so unique anyway or unstable.)
> I’ve found the link processing code on GitHub , and even the list of websites that get their own icons . I could not find a verbal description, though.
Links.js hasn't been used in years on Gwern.net. You actually want https://github.com/gwern/gwern.net/blob/959ba9c50d327a960e07... https://github.com/gwern/gwern.net/blob/959ba9c50d327a960e07... and for the history/overview, https://gwern.net/design-graveyard#link-icon-css-regexps , and to see all of the link-icons, https://gwern.net/lorem-link#link-icons
> Gwern’s website has no shortage of cool ideas. Among them showing link previews on hover. When hovering over a link, the site displays a popup window that contains a view into that page. I suspect that this view is also archived somehow, so that it retains a view into the page that matches it at the time of writing.
The archiving is complicated. Most of what you are seeing there is the use of iframes for 'live' links. (I manually check that websites do not break in an iframe before whitelisting them for popups like that.) But we do make extensive use of archives: https://gwern.net/archiving#preemptive-local-archiving
> Links to Other Sites
Gwern.net has a blogroll, incidentally. But I've always found the traditional 'big list in the sidebar' to be clunky. More fun is the 'site of the day' approach. So we went with an 'X of the Day' approach: in the footer of every page, there is a quote, a website, and an annotation of the day. (It's not really 'daily', but every few days after a full site sync.)