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.
Syncless is an experimental, lightweight, non-blocking (asynchronous) client and server socket network communication library implemented in Stackless Python 2.6. It contains an asynchronous DNS resolver (using dnspython) and an HTTP server capable of serving WSGI applications. It aims to be a coroutine-based alternative of event-driven networking engines (such as Twisted and FriendFeed's Tornado). It is already about that fast, but it has fewer features and is less stable now.
libjc is a framework for event-driven development in C. Programs that use it can perform an arbitrary number of operations simultaneously and in the background, and later wait for some or all of them to complete. The source package includes the core library along with a few objects, each of which is able to perform a set of related operations. This framework consumes significantly less memory than standard libraries, and it scales well to multiprocessor systems.
nioReactor is a framework for quickly building scalable event-driven network applications. It is built on top of the Reactor design pattern using NIO sockets. This provides high performance and allows for a complete separation from the application specific code. The goal of the project is to provide a simple set of APIs that allow users to build scalable servers without needing to deal with with the cumbersome and sometimes temperamental peaces of the NIO package.