Juju is an orchestration tool to get your code into the cloud as quickly as possible. The magic behind Juju is a collection of software components called charms. These are the encapsulated knowledge of how to properly deploy and configure the services you will want to deploy on your cloud.
The charms available online in the Charm Store represent the distilled DevOps knowledge of experts, and they are freely available for you to use (or you can write your own). You can deploy these services via the command line, or via a comprehensive web interface on Amazon Web Services, HP Cloud, Microsoft Windows Azure, your own OpenStack, and even your local computer.
Charms make it quick and easy to reliably and repeatedly deploy services in your cloud. If you haven’t already tried the Juju walkthrough, you should give it a go and see how ridiculously easy it is to deploy services in minutes.