In doing some research for an upcoming story in Baseline magazine, I came across this handy comparison chart that shows the difference in the two VMware hypervisor versions. ESXi is for free (for the time it will take you to register). ESX is the one they charge big bucks for. Both are “bare metal” hypervisors, meaning that they install a lightweight Linux-like OS and then run the various guest VMs on top of that. Obviously, the free version lacks some big features, such as Web access to manage the VMs.