Ext is a popular JavaScript library used for building web applications. It provides a set of tools and components that help developers create interactive user interfaces quickly and efficiently. The library is designed to work seamlessly with HTML and CSS, making it easier to manage complex web projects. One of the key features of Ext is its rich set of pre-built UI components, such as grids, forms, and charts. These components can be easily customized and integrated into applications, allowing developers to focus on functionality rather than starting from scratch. Overall, Ext enhances productivity and streamlines the development process.