Sensu by Pat Cable
From the description of the April 2013 BBLISA meeting at http://www.standalone-sysadmin.com/bl...
Pat Cable showed up to talk about Sensu, a ruby-based monitoring solution that uses AMQP queues to distribute tasks around a monitoring infrastructure that can scale out horizontally to monitor extremely large numbers of machines. It's definitely a "next gen" monitoring solution that you should be aware of.