Fastify.js is a web framework for Node.js that provides developers with flexibility and speed. It is lightweight, fast and low-overhead, making it perfect for creating high-performance APIs and web applications. Fastify.js also comes with a powerful plugin system that allows developers to easily extend the capabilities of the framework, and it provides a set of core features that make it easier to develop and maintain web applications. With its impressive performance, easy-to-use plugin system, and great set of core features, Fastify.js is an ideal choice for developing high-performance web applications.