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.
StoryMill - Developers and publishers of Mac, Win, and iOS productivity, home and office and writing software such as MacGourmet, Paperless and many more. Based in MN.
Markdown to PDF - Super simple way to get your markdown files to PDF
Manuskript - Open-source tool for writers.
UnMarkDocs - Unleash the Power of Markdown to Write Better Product Documentation
Novelize - Novelize is an online novel writing app designed to keep authors on track.