Markdown (US$9.99, iPad only) by David Sparks & Eddie Smith, offers a terrific introduction to the Markdown plain text-to-HTML conversion spec.
Originally created to provide an easier way to produce web content, Markdown is now an indispensable tool for developers and bloggers.
This intro text surveys Markdown and offers a reference and tutorial for both those who are new to the technology and those who want to improve their Markdown skills.
The core subject is actually quite small, so the authors have wisely focused on the bigger picture -- how do you use Markdown on various platforms and tools.
The
