Mou

Mou is a Markdown editor - with a difference: where most, if not all, currently available Markdown editors are almost all for general writers, Mou is different: It's for Web developers.

Syntax highlighting, live preview, sync scroll, fullscreen mode, auto save, powerful actions, auto pair, custom themes and CSS, HTML and PDF export, enhanced CJK support. I know, it's exactly the app you want.