I use PowerCLI to determine which VMs have not been logged into in the past 30 days. The same script then calls VC Orchestrator which emails the user to verify if the VM is needed, if not, Orchestrator moves the VMs to a specified folder then deletes them after a specified time period. I also validate with the Idle Machine report out of vcOps.
My search for a good tool to do this came up empty which is why I created my own.