SCSS is a preprocessor scripting language that extends the capabilities of CSS by adding features such as variables, nesting, and mixins. It allows developers to write more efficient and maintainable CSS code, and helps to streamline the development process by reducing repetition and increasing reusability.

PostCSS is a popular open-source tool that enables web developers to transform CSS styles with JavaScript plugins. It allows for efficient processing of CSS styles, from applying vendor prefixes to improving browser compatibility, ultimately resulting in cleaner, faster, and more maintainable code.