Softcover handles Markdown + embedded LaTeX on your local machine (no 'net connection required) using a standard text editor and web browser:
I use Softcover to write and maintain both the code-heavy Ruby on Rails Tutorial (http://railstutorial.org/book) and the math-heavy Tau Manifesto (http://tauday.com/tau-manifesto). (Disclosure: I'm also the principal author of Softcover.)