The main feature of responsive web design frameworks is their ability to create websites that adapt seamlessly to different screen sizes and devices. This approach utilizes flexible layouts, grid systems, and media queries to ensure that users have a consistent experience, regardless of whether they are accessing the site from a desktop computer, tablet, or smartphone. Responsive design is crucial for enhancing user experience, improving SEO rankings, and reducing bounce rates. By prioritizing mobile-friendliness, these frameworks help businesses reach a broader audience in an increasingly mobile-driven world.