RunJRun is a very simple system for doing parallel processing in Java, using Amazon Elastic Compute Cloud (EC2) instances as compute nodes. The basic compute unit is a Runnable, Serializable Java object, a "task" for short. A user submits a list of such tasks to RunJRun. Each task then has its run() method invoked on an EC2 instance. To use it, you'll need an Amazon Machine Image (AMI) that has the RunJRun server-side software installed; several such AMIs are available.