rST (short for reStructuredText) is a simple document syntax from which you can rapidly generate rich PDFs, link-laden HTML pages, and a variety of other formats on the fly. One of the optional projects for Acquia U has been to review and update an internal course manual on Drupal 7 Module Development, which is written in reStructuredText.
Here's a Gist with sample rST. I used TexLive to convert the code from this Gist into the below PDF (added as an attachment).
Sphinx is a library that