Can we use this question to collect information and the pros and cons of each of the above products?
Specifically I am wondering whethere there is any sane reason to use Hyper-V (the role built into Windows Server) over Hyper-V server (the stand-alone product based on the same technology) and what exactly the differences are between ESXi, Xen and Hyper-V and why nobody seems to use Parallels Bare Metal.
Make this a Community Wiki. I want comparisons, not reputation.