As a Content Management Framework Symfony CMF is not a complete CMS product, but more of a framework to build your own CMS on top of. This makes it stand out from the crowd.
The Symfony CMF project delivers developers a set of tools to create a Content Management System. This means that in order to get together the basic functions of a CMS, you'll need to spend quite a bit of time yourself to do this - the reward is that you've got complete flexibility for doing this.
The Symfony Content Management Framework also chooses to abstract the core functionalities such as the Content Repository to other projects that provide this. The CMF does not come with it's own SQL implementation of a database layer to manage content, but instead relies on other tools like PHPCR, Jackalope or the Java powered Jackrabbit.
The Symfony CMF is ready to be clustered using Docker or other options thanks to the architecture and the great bundles available in the Symfony ecosystem. An example of a CMS built with the Symfony CMF is the Sulu project.