VMware Update Manager is a native plugin for vCenter allowing the creation of defined patch base-lines which are automatically (scheduled) applied to host for ESX updates (using maintenance mode for seamless updates)
vSphere 5 introduced the ability to have concurrent updates on multiple hosts or even (where downtime is less important than update time) to update all hosts concurrently. It also facilitates the upgrade from ESX to ESXi and enhances VMware tools upgrades (less reboots) and enhanced virtual appliance upgrades.