TYPO3: TYPO3 is an open-source content management system (CMS) that is licensed under the GNU General Public License (GPL). It is a powerful and feature-rich CMS that is used for creating and managing complex websites and web applications.

TYPO3 is known for its flexibility, scalability, and extensibility. It includes a wide range of features and extensions that can be easily integrated into the platform, allowing users to create unique and personalized websites and web applications.

One of the main advantages of TYPO3 being open-source is that it allows users to access and modify the source code, which can be particularly useful for developers who require a highly customizable content management system. It also enables developers to contribute to the development of the software and help improve its functionality and security.

TYPO3 also benefits from a large community of users and developers who create extensions and templates that can be easily integrated into the platform. This allows users to add additional features and functionality to their websites and web applications without needing to write code from scratch.

Overall, TYPO3 being open-source has contributed to its popularity as a content management system. Its flexibility, scalability, and extensibility make it an attractive option for individuals and organizations looking to create complex websites and web applications. Its open-source nature also allows developers to contribute to its development and help improve its functionality and security.