I enjoyed using Asciidoctor to write a book. It necessitates using a text editor instead of a word processor so it doesn't fit DJ's use case, but it really is quite nice.

I'm also fascinated by the build for Ada & Zangemann, a FOSS illustrated full-color children's book. It looks rather complex, but it handles translations, beautiful typesetting, and was remarkably fast when I tried running the build locally.