Pressbooks

 Pressbooks  is a book content management system which produces multiple formats: ebooks, webbooks, print-ready PDF, and various XML flavours. Pressbooks is built on top of WordPress Multisite.

The open source version of the plugin is available on GitHub at https://github.com/pressbooks/pressbooks.

Various hosts will maintain and manage versions or even subsets of the service including:
 * https://pressbooks.com/
 * https://reclaimhosting.com/pressbooks/