Keystone.js is a Node.js-based content management system (CMS) that leverages Express.js for its backend and supports both MongoDB and PostgreSQL databases, offering flexibility and customization similar to WordPress. It provides robust GraphQL support, allowing developers to define schemas easily and generate related CRUD operations, which simplifies database interactions and saves development time. The CMS features an adaptable admin user interface that automatically adjusts based on user-defined schemas, enhancing ease of data management. A tutorial demonstrates building a movie rating app using Keystone.js, illustrating its capabilities in handling data schemas, integrating with GraphQL, and creating user interfaces. This process involves setting up a project, creating a data model, and building a static website to interact with the data, highlighting Keystone.js's efficiency in developing dynamic applications.