It served me well for several years, and as far as I know, it’s once again in active development.
From the same company comes ØMQ, a messaging system that is fast, scalable and simple to use:
This little library is really fast, and you can learn to use it in about one hour. ØMQ does the hard work of messaging behind the scenes. It’s portable, runs on lots of operating systems and has loads of language interfaces. And your apps stretch to many cores, and many boxes, like magic. Connect your application threads and processes together using message patterns like request-reply and pubsub. Patterns are building blocks you can use individually, or connect in many ways. You access ØMQ using a simple socket API. From any language and on any OS (almost).
Ada programmers will be glad to know that ØMQ comes with a complete Ada binding, which appears to be very easy to use.
My experience with iMatix software is that it is performant and stable, so if you need a messaging system, this just might be it.