I'm wondering is there any open-source solution for web-book creation like "The Django Book" has?
It has a really usable web interface, comments system (with comments targeted on certain peace of text), pdf nightly auto-generation, with whole content pulled from repo...
The Book module that forms a part of Drupal Core is reportedly a pretty good tool for collaborative book authoring.
Caveat: While I've used Drupal to create a couple of websites, I've not used the Book module myself.
The only Django based one I know of is openbookplatform but it is an abandoned project and hasn't even been updated for Django 1.x. However, it might be a good starting point.