The document compares Xen open source virtualization software to Citrix XenServer 5.0. XenServer provides more stability, security, and support than the open source Xen through features like automated patching, high availability options, and integration testing. It also supports more guests, CPUs, and memory than Xen. Citrix enhances Xen with its own proprietary functionality and provides a more complete virtualization platform than the Xen community through products and support.