vSphere is the management tool that you need to install to use and manage VMware ESX and VMware ESXi.
You use vSphere to install the virtual image file (.ova) for NetScaler Gateway on VMware. You also use vSphere to configure the basic settings of the virtual appliance. For details, see Configuring NetScaler Gateway VPX for the First Time.
For more information about vSphere, see the vSphere documentation.