Stylizer - A productivity-focused real-time CSS editor for serious web developers. Mac OS X and Windows.
Markdown by DaringFireball - Text-to-HTML conversion tool/syntax for web writers, by John Gruber
EnjoyCSS - CSS generator for rich graphical styles without coding
Typora - A minimal Markdown reading & writing app.
Rapid CSS Editor - Rapid CSS editor is quick, powerful and easy to use HTML and CSS code editor for web developers. Intuitive interface and intelligent features help you become more productive and create modern HTML5 and CSS3 based websites faster and easier.
StackEdit - Full-featured, open-source Markdown editor based on PageDown, the Markdown library used by Stack Overflow and the other Stack Exchange sites.