Hypothesis is a really interesting platform, but in my mind it's kind of too community-focused. Hypothesis's restricted groups (https://web.hypothes.is/help/annotating-with-groups/) are closer to what I think people would want, but to get them you'll have to self-host.
Not trying to throw shade at them, but I feel like their push for annotations is hampered a little bit by how much their specific implementation of accounts and permissions feels like yet another social network, with all of the negatives that entails. There are other issues as well, but that's the big one that kept me using the platform.
That being said, there is also an Open standard for this stuff that I remember at the time it came out being pretty excited about. But I haven't seen much if any adoption of it, so it again makes me wonder if there's something wrong with it or if it's just that nobody has made anything super-attractive yet to take advantage of it.
Which standard is that? ePubs, for example, use canonical fragment identifiers, which could also work on HTML. I think hypothes.is uses them too but adds fuzzy matching fields so that they can match up after document changes. At least from what I remember
I'm working on an annotation project myself, though not really related to what the parent commenter is looking for. A generic solution to the highlight/annotation problem is quite difficult, especially if you allow for document changes.
I read through the docs when they first came out but I don't remember all of the details anymore. Fragment identifiers are part of it though. I've gone back and forth on how much I like them, allowing for document changes is always going to make stuff really complicated, fuzzy/fragment matching is about the best you can do I think without the cooperation of the source you're annotating.
It feels like annotations probably should be tied to specific document versions, but I also get the reasoning why they're not in this proposal. Unless you're self-hosting everything or forcing everything to go through the Internet Archive... it's just kind of difficult.
I've been curious about trying to get annotations to work before using something like Matrix to handle accounts/groups, but not curious enough to actually try to build a working example.
