While I have not looked especially far and wide, I haven't found a book publishing toolchain that I like which both has a nice workflow AND does not rely on a ton of heavyweight dependencies. Since I have a real need for outputting nice documents in PDF, ePUB, and MOBI format, I am going to experiment with building a tool that fits my personal tastes and workflow.
My initial goal is just to mess around with parsing a tiny subset of Markdown into Ruby objects. Once I've got that far, I'll work on a proof of concept PDF outputter, probably using Prawn. If I make it that far without discovering some obviously better tool or deciding that this is going to be a huge time sink, I'll re-visit this document and put together a proper release plan.
PDF can be generated out of the box after installing the bookie gem. For ePUB, it's necessary to have the GNU zip command line utility present (preinstalled on OS X and many linux distros, but you may need msys on Windows, not sure.). For MOBI, you need to install kindlegen manually.
A long term goal for this project would be to eliminate most or all of these non-ruby dependencies, but I want to get a working toolchain together first.
I'm happy to accept contributions to this project, but probably won't have a formal process for doing so until I've gone beyond the proof of concept phase. Please do catch up with me if you have questions, suggestions, or ideas though. I am @seacreature on Freenode and twitter, and my email address is firstname.lastname@example.org.
Bookie is Free Software, available under the GNU General Public License (v3). Please see the GPLv3 file for details, and feel free to contact me if you have any questions