WMD is a simple, lightweight HTML editor for blog comments, forum posts, and basic content management. This editor is developed by John Fraser of AttackLabs.
You can add WMD to any textarea with one line of code. Also you can add live preview with one line more. WMD works in nearly all modern browsers.
Wysiwym stands for What You See Is What You Mean. WMD produces clean semantic HTML, leaving presentation details like fonts and colors up to style sheets. WMD’s live preview shows you exactly what your text will look like after the current styles have been applied.
Stackoverflow.com is using this editor and since it was having some outstanding bugs and issues, Chris Jester-Young has re-written the code. The modified code is hosted on Git hub.