Apache Qpid is a messaging broker that implements the latest AMQP specification, providing transaction management, queuing, distribution, security, management, clustering, federation, heterogeneous multi-platform support, and much more. It is extremely fast and aims to be 100% AMQP Compliant.
HornetQ is a multi-protocol, embeddable, high performance, clustered, asynchronous messaging system. HornetQ is an example of Message Oriented Middleware. It includes an extensive, easy-to-understand user-manual and quick-start guide and over 65 ready-to-run examples out of the box, demonstrating everything from simple JMS usage to complex clusters of servers and more exotic functionality. Its elegant POJO based design has minimal third party dependencies. You can run HornetQ as a stand-alone messaging broker, run it in integrated in your favorite JEE application server, or run it embedded inside your own application. Its journal provides high persistent messaging performance. Automatically switching into native mode when running on Linux, it uses asynchronous IO to provide persistent messaging rates that can saturate the write throughput of a disk. Its pluggable transport system uses JBoss Netty out of the box to provide high performance and scalability on the wire.