Tree - Write documents in tree-like organisation with Markdown
Array - "Need a multi-user database application? Code it with HTML/OS.
NotePlan - Make plans inside an individual markdown note for every day in your calendar. Use it as a journal for your daily tasks and plan todos in advance. For Mac, iPhone and iPad.
Markdown Here - Google Chrome, Firefox, and Thunderbird extension that lets you write email in Markdown and render...
UnMarkDocs - Unleash the Power of Markdown to Write Better Product Documentation
Caret - Better Markdown Editor for Mac / Windows / Linux