The Lightning App Builder is a drag-and-drop tool that allows Salesforce users to create custom applications and user interfaces without the need for coding. It is a visual development environment that enables users to design responsive and mobile-friendly applications for desktop and mobile devices.

With the Lightning App Builder, users can create custom pages, dashboards, and components, and then arrange them using the drag-and-drop interface. It also allows users to add custom branding and design elements to their applications.

The Lightning App Builder is a powerful tool for developers and non-developers alike, as it provides an intuitive interface that streamlines the application development process. It helps organizations to create customized user experiences that are tailored to their specific business needs.