Right from the ESXi features page:
" VMware vSphere Client. Manage VMware ESX or ESXi hosts, virtual machines and (optionally) VMware vCenter Server with the common user interface of the VMware vSphere Client. The vSphere Client is available as a free download and can be pointed at a VMware ESX or ESXi host for single host management, or it can be pointed at VMware vCenter Server for multi-host management. "
Open a web browser and type in the IP of the ESXi host and there should be a link to download the vSphere client.