CSS is described as 'Cascading Style Sheets (CSS) is a simple mechanism for adding style (e.g., fonts, colors, spacing) to web documents' and is an website in the Development category. There are four alternatives to CSS, not only websites but also apps for a variety of platforms, including Mac, Windows, Linux and Self-Hosted solutions. The best alternative is Sass, which is both free and Open Source. Other great sites and apps similar to CSS are Stylus (Free, Open Source), LESS (Free, Open Source) and WHATWG (Free, Open Source).
Sass is a stylesheet language initially designed by Hampton Catlin and developed by Nathan Weizenbaum. After its initial versions, Nathan Weizenbaum and Chris Eppstein have continued to extend Sass with SassScript, a simple scripting language used in Sass files.