One of the best things about Linux is how easily you can throw together a few tools and end up with a great system. This is especially true for provisioning VMs. Arguably, this is one of the key things that keeps me on a Linux desktop for my day-to-day work! However, these tools can also be used to turn an old laptop or desktop into a screaming hypervisor.
Link: Linux Hypervisor Setup (libvirt/qemu/kvm)