Alpine.js is a lightweight JavaScript framework designed for building interactive user interfaces. It provides a simple way to add dynamic behavior to HTML without the complexity of larger frameworks like React or Vue.js. Alpine.js uses a declarative syntax, allowing developers to define interactions directly in their HTML markup. The framework is particularly useful for projects that require minimal JavaScript but still need interactivity. With its small footprint, Alpine.js is easy to integrate into existing applications, making it a popular choice for developers looking to enhance user experience without significant overhead.