Iirc it's totally free and clones different amazon AWS API by integrating Eucalyptus (http://open.eucalyptus.com/).
The problem is, that you need to rent/buy the maximum hardware size of your could upfront as amazon does it. Therefore it's a bigh myth you only pay what you use because the provider has to split all costs+interests among the customers (like EC2). Including costs of hardware/infrastructure not currently in use!
If you have your own rack(s), tools like eucalyptus/ubuntu cloud can help you to dynamically scale your apps and use your hardware more efficent.
But remember: To do this it needs more than some instant-on virtual machines: You need to be able to automatically spawn applications with tools like puppet or chef, too. This usually requires some amount of work and brain :-)
Claiming to be able to scale to infinity just because you're using EC2/Eucalyptus/OpenStack is a biiiiiig common lie.
The web-site doesn't appear to provide a potential customer with the information they need to evaluate the service. At least, not easily.