You can use the vSphere Client (C# version) to manage your free vSphere Hypervisor, but with the feature level of version 5.0, this mean that all new features will be available only on vSphere Web Client, and to get the vSphere Web Client you will need vCenter Server, and vCenter Server cannot manage a free vSphere Hypervisor.
vCenter Server is available also as appliance, installed on top of SUSE Enterprise Linux, but again, you have to pay for it.
Anyway, if you're using the free vSphere Hypervisor, I doubt that you will need advanced (new) features that can be found only with the payed version and with the vSphere Web Client, so the vSphere Client is enough to your administer your free vSphere Hypervisor.
If you're really needing do something on your free vSphere Hypervisor and can't accomplish using the vSphere Client, tell us and we can found an alternative method, like command line.
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Richardson Porto
Senior Infrastructure Specialist
LinkedIn: http://linkedin.com/in/richardsonporto