JS-Collider is an event-driven Java network NIO framework. It is designed to provide maximum performance and scalability for applications having not too many connections but significant amounts of network traffic (both incoming and outgoing). Performance and scalability are achieved via lock free algorithms and atomic states usage. It supports UDP (with multicast) as well. One of the implementation points is to avoid unsafe cheating; it should work the same way on all JVMs (Java 1.7). It supports shared memory IPC.
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.
librouteros is a library that can be used to communicate with devices running RouterOS, a Linux-based operating system by MikroTik. A generic and low-level interface is provided to issue arbitrary commands to the device and receive replies. For some commands, high-level abstractions are provided to simplify communication. The library is thread-safe and reentrant-safe.