The entire Concrete command and transport system is built on Symfony Messenger. Concrete adds its own layers of configuration on top of Symfony Messenger, ensuring that the various transports and command handling are wired up in a way that makes sense to Concrete developers, but the underlying components are from Symfony and unmodified.
With advanced configuration it’s possible to create your own buses, route commands in adventurous ways, add custom middlewares for logging or any purpose. If any of these are options you’d like to explore with the Concrete command system, it’s highly recommended that you read through the Symfony Messenger documentation.