CSS preprocessors are tools that extend the functionality of CSS by introducing features like variables, nesting, and mixins. They enhance the maintainability and organization of stylesheets. Here are some popular CSS preprocessors:

Sass (Syntactically Awesome Stylesheets):

Sass is one of the most widely used CSS preprocessors. It introduces features like variables, nesting, and mixins. SassScript is the scripting language in Sass.

LESS:

LESS is a backward-compatible language extension for CSS. Features include variables, nesting, and mixins. It is developed to be similar to Sass but with a simpler syntax.

Stylus:

Stylus is a preprocessor that aims to be more flexible and feature-rich. Syntax is minimalistic and indentation-based. It also supports variables, nesting, and a wide range of functions.

PostCSS:

Unlike Sass or LESS, PostCSS is not a preprocessor but a tool for transforming CSS using plugins. It can be extended with various plugins for linting, autoprefixing, and more.Offers a modular and customizable approach to enhancing CSS.

SCSS (Sassy CSS):

SCSS is an extension of Sass that uses a CSS-like syntax. It maintains compatibility with CSS syntax, making it easier for CSS developers to transition to SCSS.