SASS: CSS with superpowers. Sass is the most mature, stable, and powerful professional grade CSS extension language in the world.

Source Site: https://sass-lang.com/

• Rules and Directives
• Control Directives & Expressions
• Mixin Directives

List of compliers

• CodeKit
• Koala
• Scout-App
• Winless-Window GUI for less.js
• SimpLess
• Sassmeister- The SASS Playground
• TheSassWay- Connect with information
• Compass- CSS Authoring Framework (Most preferred)
• Prepros
• LiveReload- Strong and Stable
• Compass.app- GUI compatible