Apache Qpid is a reliable, asynchronous messaging system that supports the AMQP messaging protocol in several common programming languages. Qpid is supported on most common platforms.
On the Java platform, Qpid uses the established Java JMS API.
For Python, C++, and .NET, Qpid defines its own messaging API, the Qpid Messaging API, which is conceptually similar in each.
On the .NET platform, Qpid also provides a WCF binding.
Ruby will also use the Qpid Messaging API, which will soon be implemented. (Ruby currently uses an API that is closely tied to the AMQP version).