The “key product” is GSX server – their “lower end” software that runs on a Windows or Linux server. The re-branded product is now sinply called VMWare Server, and is completely free.
My guess is that with competition from the open-source efforts like Xen and OpenVZ, they want to get you hooked on their products, in hope that you will eventually upgrade to their more advanced ESX Server. No matter if you pick an open-source or commercial product, the cost to virtualize your servers is now officially $0.00! (With VMWare server annual support starting at $300, it’s still a great deal!)