StackEdit is a free, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.
Rich Markdown editor StackEdit’s Markdown syntax highlighting is unique. The refined text formatting of the editor helps you visualize the final rendering of your files.
WYSIWYG controls StackEdit provides very handy formatting buttons and shortcuts, thanks to PageDown, the WYSIWYG-style Markdown editor used by Stack Overflow.
Smart layout Whether you write, you review, you comment… StackEdit's layout provides you with the flexibility you need, without sacrifice.
Live preview with Scroll Sync StackEdit’s Scroll Sync feature accurately binds the scrollbars of the editor panel and the preview panel to ensure that you always keep an eye on the output while writing.