Gemini enables online books that can be linked to:
Example: Dayton Experiment Hyperbook
In this example, each page is a handful of paragraphs linked to other pages. There are no chapters per say, in the sense of a large grouping of pages. Perhaps in this case you could call each page a mini chapter that is easy to link to.
For example, I was reading this book and wanted to share one interesting page to my partner. This was easy, I just copied the link to her:
gemini://jb55.com:1966/dayton.fed.wiki/calebs-story
She opened the page with Lagrange on her phone and started reading the part of the book I found interesting. I've been doing this with many other pages as well. This made me think how nice it would be if I could do this with any book I was reading. We need more books on gemini!
The problem with traditional ebooks is, how would you be able to link a specific section of a book to someone? As far as I know there is no way to do this. You would have to somehow get them to download the epub and go to a certain page. Very annoying.
Why not bring the power of hyperlinked documents to books?
Of course you could do this with html, but it's notoriously hard to make a good reading experience on the web across many different devices: mobile, desktop, etc. Gemini really shines here.
Another aspect of Gemini books is that they can be non-sequential, branching off into pages with skippable ancillary information. For example, one chapter might be talking about how they implemented the Agile methodology in the classroom, and then provide a link to a page about Agile itself. You can jump back and continue reading the main branch once you're done.
One downside is that it requires internet connectivity, but perhaps that will become less of an issue once we have an offline version of gemini based on git, which people have been talking about in geminispace lately.
One thing we could do is start converting existing open-source books to gemini. One idea I had was TAOUP: The Art of Unix Programming. Right now you can find this online in html:
http://www.catb.org/~esr/writings/taoup/html/
It would be great if there a was a gemini version of TAOUP. The chapters are already broken down in a granular enough way to fit nicely into this format. Apparently the original format was written in DocBook but I can't seem to find this online anywhere. A DocBook to gemini converter might be interesting, if people still use DocBook for books...
There could be other ways of implementing books on Gemini, but I have been enjoying the hyperbook format so far. I'm interested to see what other people can come up with, and more longform content on gemini in general.