ActiveMQ is a message broker enabling to support different messaging options. It will provide you high availability, performance, scalability, reliability and security for enterprise messaging. And it allows you to mediate events between distributed applications, guaranteeing that they reach their intended recipients.
Once Talend ESB installed, you can either access a standalone instance of ActiveMQ in the <TalendESBPath>/activemq directory or install it as a Feature directly within the Talend ESB Container.
Once installed, ActiveMQ can be used in Talend's Mediation routes, for example.