VMWare

Below are the alternatives

Proxmox VE - http://www.proxmox.com/

http://www.openstackready.com

http://www.xen.org/

http://www.linux-kvm.org/

I need in window based

I think the most basic info is what kind of requirements you have...and you what is your current status....
For me i have used a 2nd hand server for less than $1000 with 2x6-core XEONs and massive 48 RAM....the disk were not my concern because i already had a SAN but you could get a nice deal also on the disks..
Vmware ESXI Free Edition while it lacks some features it has all you need to host and run all kind of VMs...and for some of the hidden/inaccessible features Vmware Vsphere Client desktop edition works just fine (i have ESXI 6)...
Right now i host a dozen of VMs ranging from 8core/24gb SQL server to tiny 1-core 1gb test machines...
Also a great alternative is Microsoft Hyper-V server....totally free with more features than the locked down Vmware ESXI but habits are habits....and so i am using VMware...

Windows Server 2012/2016 and add the Hyper-V role.

What's also wrong with using VMware vSphere Essentials at approx $600 USD ?

What features do you want to use ?

Just very basic features like I can allocate hard drive and ram for each vm.

Each vm will host window server 2012 or 2008 with ms sql 2012 and visual studio 2017

It is more like for developer

All those can be done with the FREE version of ESXi, or the basic Essentials version.

Can you show me the free download link?
I actually need to save in USB flash drive to boot up
Hp pro g6 server. Anything else I should pay attention?

You do know that even though you said "Windows based" Vmware is actually a Linux core?

You don't need windows to run virtualized Windows...

Do you require any additional help, to select and accept a solution to this question?