The framework widely used for building scalable web applications is Node.js. This JavaScript runtime environment enables developers to construct server-side applications with high efficiency and speed. Node.js is event-driven, non-blocking, and allows for handling multiple connections concurrently, making it ideal for real-time applications and scalable architectures. Its extensive package ecosystem (npm) and active community support facilitate rapid development while providing ample resources for developers. Node.js is commonly used in conjunction with frameworks like Express to streamline web application development.