The Siesta framework is used to build an API-driven iOS app, specifically a Pokémon Dex, using the Pokeapi as the data source. The app fetches and displays a list of 151 Pokémon, with each Pokémon's details displayed on a separate screen. The app uses Swift and SwiftyJSON for JSON processing, and Siesta for managing resources and handling network requests. The app also includes features such as caching, status overlays, and resource observers to manage the UI and handle changes to the data. The code is well-structured and follows best practices for iOS development with Swift. The app demonstrates how to use Siesta to simplify API interactions in mobile apps.