Performance Sentry VM runs as a service in Windows Vista, Windows 7, Windows Server 2008 or Windows Server 2008 R2. It can run in a VM guest, or a machine external to the ESX host.
It connects directly to the ESX host server and using APIs retrieves the host and guest metrics and formats them into Windows Performance objects and counters viewable in Perfmon. The metrics can then be collected by Performance Sentry (NTSMF) or any other software that collects Windows performance metrics.
Performance Sentry does not require vCenter.
The following is a brief video introduction to Performance Sentry VM.