OpenAMQ is a fast, stable, free implementation of the AMQP (www.amqp.org) messaging protocol. It gives applications high-performance messaging (delivery of opaque data) across loosely connected networks. It is capable of handling up to 600k messages per second depending on the hardware, with a latency around 300 microseconds. It is multithreaded and supports C/C++ and Java on Linux, AIX, Solaris, OS/X, Windows, and OpenVMS.
The 0MQ lightweight messaging kernel is a library which extends the standard socket interfaces with features traditionally provided by specialized messaging middleware products. 0MQ sockets provide an abstraction of asynchronous message queues, multiple messaging patterns, message filtering (subscriptions), seamless access to multiple transport protocols, and more.
Bonka's Queue is an HTTP-based message queue that relates to JMS or AMQP much in the same way that CouchDB relates to traditional DBMSes. That is to say that it tries to solve a different (much simpler) problem and avoid all the extra overhead associated with more "proper" solutions.
PICI-NMS is an object oriented middleware which makes possible sending messages in a networked environment or on a single host between applications using the library provided. The supported message sending mechanism is "publish/subscribe" and this is backed up by a very easy-to-use and intuitive C++ API which hides the underlying socket interface to make the message sending as transparent to the client as possible.
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.
TurnKey ejabberd Appliance is a server appliance that combines ejabberd with Speeqe to create a live chat server that supports strong encryption and works with any Web browser or XMPP client. ejabberd is a powerful XMPP server that supports clustering, live upgrades, shared roster groups and provides support for virtual hosts. It is designed to be easy to use and easy to maintain. Security patches are automatically installed. It provides a Web management interface, configuration console, and an AJAX Web shell. To minimize footprint the appliance is built from the ground up with the minimum required components. It runs everywhere thanks to multiple build formats, including an installable live CD, a VMDK with OVF support, and an Amazon EC2 AMI.