POSTCSS is one of the biggest ‘alternatives’ to Sass, Less and Stylus when it comes to preprocessing based on its approach – it leverages a modular plugin system that allows the user to customise their feature set and compilation as much as they want. This means that rather than just adopting a library in its entirety, you get to choose what it’s made of. Unlike many other preprocessors, POSTCSS makes no assumptions about the features or stack that you’re using. Instead, you simply add the plugins that you would like based on the features you want to use. You can add plugins to give it the exact same features as a library like Sass. Due to this modular approach, it means that you can even use plugins completely by themselves, such as auto-prefixing and minification, rather than building a full library.