The "free" one is indeed the vSphere Hypervisor which your can download from Download VMware vSphere Hypervisor for Free
Yes you will get a free Licensekey during the download because the "Software" is always the same and the features will be acticated by the licensekey.
Alle the other stuff is the $$$ one and called vSphere ESXi and vCenter(central management). Different bundle and editions. Iam sure there is an edition overview on vmware.com.
Regards,
Joerg