Typora - A minimal Markdown reading & writing app.
WriteWell - Jumpstart your writing with the world's best templates.
Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
Ulysses.app - A powerful writing tool for Mac, iPad, and iPhone
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
Daily Prompt - Become a better writer