Cloud interoperability--the ability to abstract the programmatic differences from one cloud to another--is a key to adoption. If we assume that some percentage of private compute clouds will be based on virtualization, and we know that a large percentage of public clouds already are, then the ability to move among virtual machines is a critical function in this regard.
Deltacloud, a new open-source project "designed to enable an ecosystem of developers, tools, scripts, and applications that can interoperate across the public and private clouds."
Deltacloud gives you:
* REST API (simple, any-platform access)
* Support for EC2, RHEV-M; VMWare ESX, RackSpace coming soon
* Backward compatibility across versions, providing long-term stability for scripts, tools and applications