I disagree - VMWare is available for Linux, Windows and MacOS. Xen is another option, available for Linux, as is KVM and several others. To be able to run Xen with Windows as a guest-OS or KVM (at all) you need to have a processor with virtualization extension, such as AMD Socket F or AM2 or better - and Intel has very similar features in their processors of similar age.
I think Parallels is the ONLY virtualization software that is directly written for MacOS.
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Mats