Cloud.com contributes code and development help to OpenStack, and uses OpenStack as part of its CloudStack partially open/partially proprietary infrastructure.
It tries to set itself apart with additional layers such as CloudStack Business Logic – which lets service providers using CloudStack as their platform bill for the privilege.
It also provides connections and support for other clouds using AJAX clients, APIs of its own, and a module called CloudBridge that's designed to integrate CloudStack with Amazon's EC2 using SOAP and REST to translate EC2 API commands into native CloudStack commands.
Cloud.com also supports three major virtualization platforms – Vmware's vSphere, the open-source Xen owned by Citrix, and KVM hypervisors.
The potential to share workloads between clouds, or move workloads from one to another is still at least a year off – more likely two or three. Being able to exchange data and execution requests is a major step, though.
So is the potential to use open-source code to build a private cloud without mortgaging the company to one of the big hypervisor vendors.
A December InfoWorld test of five private-cloud products made it clear building a cloud under any circumstances is no picnic.
Trying to do it, right now at least, using immature open-source software, would be the kind of adventure you probably don't want to bet your career on.