I see a difference with a message broker that has message queuing and just a listener to events. What exactly do you mean with a listener for events?
By default mendix allows you to use webservices, however as you might know this does not queue your messages nor does it allow you to use a common data model. Thus if you need to connect to multiple applications you will require n point-to-point connections.
As for an ESB solution, we developed IRIS which is an ESB developed in Mendix based on the Spring integration framework. Because it is integrated in Mendix it allows for easy configuration and easy integration (e.g calling microflows directly from your message flow).
If you would like some more information you can mail email@example.com to request a fact sheet or additional information.
We've built our own ESB which is part of the Mendix Runtime.
Most (internal) Mendix applications are talking with each other using the MxIntegrator, which is some kind of ESB as well.