TYPO3 is a widespread Content Management System (CMS) in Germany, Switzerland and Austria. It is published under the General Public License (GPL). So there are no license fees for the use of TYPO3.
Summary of the advantages:
Because of the big community TYPO3 is continuously further developed. New requirements are realized quickly by the big amount of developers and weak points are fixed promptly. The Long Term Support (LTS) of TYPO3 guarantees the support of special versions for several years.
In Germany regarding the Open Source marked only the Content Management System Wordpress is used more frequently. Many agencies are specialized in TYPO3 an a lot of editors have experience with the system. For innumerable extra needs programers have developed extensions which can be integrated for free.
The TYPO3 backend can be adjusted to the needs of each customer. Individual requirements can be realized by custom modules which can be integrated smoothly in the current system. Unused elements can be hidden to prevent the user from being destracted.
TYPO3 offers a wide assignment of permissions. Depending on the user or the user group you can define which modules, content elements or extensions an editor can see. The adjustments are that specific that even single fields can be shown or hidden.
TYPO3 can define various workspaces, in which content elements can be created. In a simple example, there would be a test workspace (visible to editors) and a live workspace (visible to the website visitor as well).
After being tested successfully contents can be moved from the test workspace to the live workspace. Furthermore, it is possible to allow this publishment only to special editors. Even complicated workflows in which contents have to follow a long review process can be realized with TYPO3.
The contents can be created with a start and an end date in TYPO3. Thus the period is defined in which contents are visible for the visitor of the website.
In-between most of the users regard websites with their mobile devices. So the creation of responsive websites is normal in these days. The strict separation of content and design in TYP3 makes it easy to create mobile versions.