Repeater app is a new tool on the Contentful App Marketplace that helps developers repeat content in a flexible way, allowing them to create custom lists of items or products using JSON fields. The app was built using the App Framework, Forma 36, and TypeScript, and provides a range of features such as automatic resizing, UI components, and hot reloading. It can be easily extended and customized by developers, and is available for free installation on the Contentful App Marketplace. The app is designed to work with Contentful's JSON fields, but also allows for reference fields, and can be used to create powerful repeater apps with custom UI/UX components.