If you don't know what VMware ESXi is, you probably don't care about this post. If you do, though, you might have found it difficult to obtain a serial number for your copy of ESXi. Although ESXi is free, it has a 60-day limit on running unregistered.
Thing is, if you visit the www.vmware.com site, it isn't immediately obvious how to get a serial number. Seeing how it's a free product, you would think it would be easy. It isn't. Here is what I did:
You had to create an account to download ESXi, so log in with that account. If you did like me, you probably forgot the password, so use the "forgot password" link to get it back. Okay, so you log in. Once logged in, visit https://www.vmware.com/tryvmware/p/activate.php?p=esxi. That should get you right to the serial number page for ESXi.
If that didn't work, you could do this instead: Once logged in, visit the main www.vmware.com page. Off to the right-hand side under "Datacenter Products" they do have an "VMware ESXi" link. Visit it. You will be asked to click "Continue". Do so. Eventually you'll get to where you get the serial number from.