ESXi is free, but usable on one system. ESX is the full-blown version, costs, and I *think* comes with the console... which, for some unknown reason, is WinDoze *only*.
I believe both can be administered via browser.
maybe because there are more windows users that Linux and / or Mac OS X and FreeBSD.
i have read in [1] and [2] that even RedHat may do the same thing (a Wind0w$ only console)
[1] http://www.internetnews.com/software/article.php/3847391/Red+Hat+Virtualizat...
[2] http://www.linuxtoday.com/it_management/2009110700635NWRH
I' m not sure but it will be helpful if someone confirm (or not).
Best regards.