RVtools is a great tools to inventory a virtual infrastructure based on VMware vSphere, with or without vCenter Server (works great also on standalone ESXi hosts). RVTools supports ESX Server 3.5, VirtualCenter 2.5, ESX Server 3i, ESX Server 4i, VirtualCenter 4.x, ESX 4.x, VirtualCenter 5.0, VirtualCenter Appliance, ESX 5.0, VirtualCenter 5.5, ESX 5.5, VirtualCenter 6.0, ESX 6.0, VirtualCenter 6.5 and ESX 6.5, so all you can have (also legacy versions) in a datacenter. And it’s totally free.