"a Scala 2.8 based messaging broker. It can be thought of as a forked and stripped down version of Apache ActiveMQ . It is focused on providing a simple, stable, scalable messaging core which is easy to extend."

"a simple, fast workqueue service"

"simple, reliable, mid-scale p2p messaging and storage"

"provides web applications with enterprise-level messaging via an asynchronous RESTful interface that works over standard HTTP/HTTPS"

"enable rapid development of applications that process large volumes of incoming messages or events. Esper and NEsper filter and analyze events in various ways, and respond to conditions of interest in real-time"

"a simple to use publish/subscribe messaging system for HTML/JavaScript applications, empowering event-driven UI development in the web browser"

"In hopes of saving others a knock or two, we have tried to collect here background information and commentary on some of the issues involved in successful deployments."

"an Objective-C implementation of asynchronous inter-thread message passing"

Hell yes. That's what a queue API should look like.

"a pure C, very simple durable message queue with multiple subscribers and publishers (both thread and multi-process safe)"

"Our mission with ØMQ ("ZeroMQ") is to build the fastest messaging ever.

Ha! Someone scooped Blaine on the open source release of Starling, and managed to add extra features. Too funny.

Sort of like Twitter's own as-yet-unreleased Starling, but it has its own protocol rather than speaking memcache's.

How Dopplr does their message queues.

Lightweight cross-language message queue system

an open source toolkit that provides a high performance messaging service.

event-based Rails