Zuul is a browser-based test runner designed for robust cross-browser testing. It streamlines the process of executing tests in various browsers, both locally and remotely, including real browsers via services like Sauce Labs and BrowserStack. Zuul simplifies configuration, making it easier to manage dependencies and environments. This enables consistent and reliable testing across different platforms, ensuring broad compatibility and improved code quality. It particularly excels at testing libraries and applications intended for wide browser support.