I think Discord servers based around specific books are an underappreciated form of academic support/community. I have been part of such a Discord server (for Terence Tao's Analysis) for a few years now and have really enjoyed being a part of it.

Each chapter of the book gets two channels: one to discuss the reading material in that chapter, and one to discuss the exercises in that chapter. There are also channels for general discussion, introductions, and a few other things.

Such a Discord server has elements of university courses, Math Stack Exchange, Reddit, independent study groups, and random blog posts, but is different from all of them:

• Unlike courses (but like Math SE, Reddit, and independent study groups), all participation is voluntary so the people in the community are selected for actually being interested in the material.
• Unlike Math SE and Reddit (but like courses and independent study groups), one does not need to laboriously set the context each time one wants to ask a question or talk about something. It's possible to just say "the second paragraph on page 76" or "Proposition 6.4.12(c)" and expect to be understood, because there is common knowledge of what the material is and the fact that everyone there has access to that material. In a subject like real analysis where there are many ways to develop the material, this is a big plus.
• Unlike independent study groups and courses (but like Math SE and Reddit), there is no set pace or requirement to join the study group at a specific point in time. This means people can just show up whenever they start working on the book without worrying that they are behind and need to catch up to the discussion, because there is no single place in the book everyone is at. This also makes this kind of Discord server easier to set up because it does not require finding someone else who is studying the material at the same time, so there is less cost to coordination.
• Unlike random forum/blog posts about the book, a dedicated Discord server can comprehensively cover the entire book and has the potential to be "alive/motivating" (it's pretty demotivating to have a question about a blog post which was written years ago and where the author probably won't respond; I think reliability is important for making it seem safe/motivating to ask questions).

I also like that Discord has an informal feel to it (less friction to just ask a question) and can be both synchronous and asynchronous.

I think these Discord servers aren't that hard to set up and maintain. As long as there is one person there who has worked through the entire book, the server won't seem "dead" and it should accumulate more users. (What's the motivation for staying in the server if you've worked through the whole book? I think it provides a nice review/repetition of the material.) I've also noticed that earlier on I had to answer more questions in early chapters of the book, but now there are more people who've worked through the early chapters who can answer those questions, so I tend to focus on the later chapters now. So my concrete proposal is that more people, when they finish working through a book, should try to "adopt" the book by creating a Discord server and fielding questions from people who are still working through the book (and then advertising in some standard channels like a relevant subreddit). This requires little coordination ability (everyone from the second person onward selfishly benefits by joining the server and does not need to pay any costs).

I am uncertain how well this format would work for less technical books where there might not be a single answer to a question/a "ground truth" (which leaves room for people to give their opinions more).

(Thanks to people on the Tao Analysis Discord, especially pecfex for starting a discussion on the server about whether there are any similar servers, which gave me the idea to write this post, and Segun for creating the Tao Analysis Discord.)