Typora - A minimal Markdown reading & writing app.
Notezilla - Colorful & powerful sticky notes app for Windows & Phones.
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
OneNote - Get the OneNote app for free on your tablet, phone, and computer, so you can capture your ideas and to-do lists in one place wherever you are. Or try OneNote with Office for free.
MarkText.app - Mark Text is a Markdown editor for Mac, Windows and Linux.
Evernote - Bring your life's work together in one digital workspace. Evernote is the place to collect inspirational ideas, write meaningful words, and move your important projects forward.