Virtualization server vendors are following the example of systems-management and physical-server vendors by expanding their management applications to control not only their own virtual server environments, but those of their competitors.

Citrix Systems and Microsoft's management tools—XenCenter and System Center Virtual Machine Manager 2008—both manage virtualized environments based on VMware's ESX Server as well as those of their own products.

"Several of our clients are looking at using Microsoft's Hyper-V or Citrix XenServer to compliment their existing VMware ESX environment," says Chris Wolf, senior analyst for The Burton Group in Salt Lake City. "The reasoning has primarily been cost, and the other platforms provide the services they need for virtualizing branch offices as well as development, test or training environments."