Svelte.js is a modern web framework that focuses on building highly efficient and fast web applications.

It is known for its unique approach to building user interfaces, as it shifts much of the work normally done at runtime to compile time, resulting in smaller and faster code. Svelte.js offers a simple and intuitive way to create reactive and interactive web applications, and it has gained popularity for its performance and developer-friendly approach. It also provides a rich set of features for building components, handling state management, and working with animations.