You Need A Wiki - Create a wiki with Google Docs
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.
Stack Overflow Documentation - A crowdsourced developer documentation
Markdown to PDF - Super simple way to get your markdown files to PDF
Greenboard - Generate beautiful static api documentation
UnMarkDocs - Unleash the Power of Markdown to Write Better Product Documentation