Markdown Here - Google Chrome, Firefox, and Thunderbird extension that lets you write email in Markdown and render...
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.
Dillinger - joemccann has 95 repositories available. Follow their code on GitHub.
Markdown to PDF - Super simple way to get your markdown files to PDF
The Most Dangerous Writing Prompts - Don't stop typing, or all progress will be lost.
UnMarkDocs - Unleash the Power of Markdown to Write Better Product Documentation