For those attending London Realtime here are some details.
$ npm install sockjs
(and then ...)
$ gem install vmc
CloudFoundry is an open source Platform as a Service from VMware. What is platform as a service? In short, Cloud Foundry will host your web apps for you, as well as running various servers like MongoDB, Redis and yes, RabbitMQ for you as well. And it's all open source.
$ brew install rabbitmq
$ apt-get install rabbitmq-server
RabbitMQ is a messaging server that gives you a backbone for scaling realtime apps. There are many, many clients for it, for example Node.JS and Ruby. The step-by-step tutorials are a good way to get started, and have code examples for many different languages.