Given originally at http://frontenddesignconference.com.
Updated for:
• http://eduiconf.org/
• http://ncdevcon.com/
• http://www.fitc.ca/unleashed
• http://futureofwebdesign.com/nyc-2013/
An overview of the popular pre-processors: Stylus, Less & Sass, with features subdivided up into easy to learn sections of beginner, intermediate and advanced.