The programming language often used for building interactive web apps, in combination with JavaScript, is HTML. However, often developers additionally utilize CSS (Cascading Style Sheets) for styling and layout. Together, these languages form the core of web development. HTML structures the content, CSS enables the visual presentation, and JavaScript adds interactivity, creating a dynamic user experience. With frameworks like React, Angular, or Vue.js, developers can create sophisticated single-page applications that enhance user interaction.