Vivaldi is a highly customizable web browser known for its flexibility and user-centric design. It allows extensive personalization, including tab management, user interface modifications, and gesture controls. Vivaldi also emphasizes privacy and security, offering built-in ad and tracker blocking. Unique features include the ability to group tabs into stacks and to view multiple tabs in a split-screen mode. It caters to power users who desire a tailored browsing experience with advanced functionality and efficiency.