Apache ActiveMQ is an open source message broker, written in Java, together with a full Java Message Service (JMS) client.
It is the most mature implementation out of the three that we examine here, and has a long history of successful production deployments. Commercial support is offered by many companies, including Red Hat.
It is a fairly simple queuing system to set up and manage. It is based on the JMS client protocol and is the tool of choice for Java EE systems.