Almost all of the software that I have used in the creation of this book are FLOSS.
In the first draft of this book, I had used Red Hat 9.0 Linux as the foundation of my setup and in the sixth draft, I used Fedora Core 3 Linux as the basis of my setup.
Initially, I was using KWord to write the book (as explained in the history lesson in the preface).
Later, I switched to DocBook XML using Kate but I found it too tedious. So, I switched to OpenOffice which was just excellent with the level of control it provided for formatting as well as the PDF generation, but it produced very sloppy HTML from the document.
Finally, I discovered XEmacs and I rewrote the book from scratch in DocBook XML (again) after I decided that this format was the long term solution.
In the sixth draft, I decided to use Quanta+ to do all the editing. The standard XSL stylesheets that came with Fedora Core 3 Linux were being used. However, I had written a CSS document to give color and style to the HTML pages. I had also written a crude lexical analyzer, in Python of course, which automatically provides syntax highlighting to all the program listings.
For the seventh draft, I'm using MediaWiki as the basis of my setup. I used to edit everything online and the readers can directly read/edit/discuss within the wiki website, but I ended up spending more time fighting spam than writing.
For the eight draft, I used Vim, Pandoc, and Mac OS X.
Now I use Emacs 24.3 + ghoseb's dotemacs + Jason Blevins' Markdown Mode which is a beautiful combination of software. As you may have realized, I am quite happy with this editing setup.