Just look for Linux and KVM. For open-source solutions KVM typically is the way to go these days. In the past people also used Xen, but by most folks using open source that seems to have been replaced by KVM over the past couple of years.
I personally have no, or not much, experience with it as I work for VMware, but considering the amount of articles on the topic of KVM you shouldn't have problems configuring and using it. Pick a Linux distribution you are most comfortable with and go do your thing.