PostCSS

PostCSS is a CSS post-processor and syntax transformer that uses JavaScript plugins to parse and transform stylesheets. Stable version 8.x, actively maintained with monthly minor/patch releases. Key differentiators: plugin-driven architecture (over 200 plugins), supports future CSS syntax via plugins like postcss-preset-env, used by popular tools like Autoprefixer and Stylelint. Ships TypeScript definitions, supports ESM and CJS, requires Node.js 10+ (12+ for full features). Provides a fast CSS parser with source map support and a rich plugin API.