Sails.js is a popular MVC (Model-View-Controller) framework for Node.js designed to facilitate the development of custom, enterprise-grade applications. It is particularly well-suited for building data-driven APIs, as well as real-time applications. Sails.js is built on the Express framework, enhancing it with easy data modeling through its built-in ORM, Waterline, which supports popular databases like MySQL, MongoDB, and PostgreSQL. Additionally, Sails.js follows convention-over-configuration principles, streamlining the development process and reducing the amount of setup required.