As stated on the RVTOOL Site, it is a Windows .Net application which interacts with your virtual environment using the latest VI SDK to gather health and resource information about each of the ESX hosts and virtual machines. You can either connect directly to an ESX host or call out your environment via vCentre.
I have come across this tool while trying to find an easy way to examine and release a CD or Floppy Disk if mounted to any of the virtual machines, but this is only few of the many uses for this tool. The new version allows passthrough authentication, so you can use your domain username and password to login and use the tool. It also provides some new command line options.
I would recommend having a look at this tool.