Symphony CMS is an open-source content management system designed for developers, providing a flexible, lightweight framework to build custom web applications. It emphasizes extensibility and customization, allowing developers to structure their content and data models freely. Symphony is known for its minimal core, which can be extended through the use of extensions and is built on PHP. The system is designed to promote clean code and efficient development practices. Symphony's data-driven architecture uses XML and XSLT for templating, offering a high degree of control over the design and functionality of web projects.