Booktools
A little-known bit of trivia about our book, Python Web Development with Django: we wrote the manuscript in Markdown.
I think it was my idea. One of the major motivations for using a text-based format – versus the unfortunate de facto standard, Microsoft Word – was integration with good developer tools and workflow.
Our manuscript and all our project code was in a Subversion repo, so each author always had the latest updates. HTML generated from the Markdown files was great for generating nice printed/printable output too.