CSS Next - Use tomorrow’s CSS syntax, today.
rubular - A ruby based regular expression editor
Garden (Clojure) - Unlike the mini-languages that are other pre/post-processor options, Garden leverages the full power of the Clojure programming language for CSS.
RegExr - RegExr.com is an online tool to learn, build, and test Regular Expressions.
Stylus - EXPRESSIVE, DYNAMIC, ROBUST CSS
RegEx Generator - RegEx Generator is a simple-to-use application that comes with the brilliance of intuitive regex and is also helping you out to test the regex.