i know of Xen, Bhyve (which is like a vmm but with a hypervisor too, but its kinda less capable), or KVM (i don't really like GNU/Linux but ill get over it eventually i guess, im in a love hate relationship rn because distro fragmentation kinda sucks a lot)
Xen apparently may or may not work on my current hardware, unfortunately, and i also don't know if ill even benefit from it anyways, since i really don't have a problem with running a host, its 2024, i have enough computational resources for having a resource intense host
i would also say NetBSD Virtual Machine Manager is an option but i can't run NetBSD on most of my hardware as a host, and nested virtualization is not really possible on FreeBSD Bhyve iirc, and id rather not do a QEMU/KVM setup just to run NetBSD, it would be really heavy and sluggish for the most part, but idrk
plan 9 also has a virtual machine system, but i don't really have a reason to start a 9fs grid since im broke af and can't buy a bunch of machines, so yeah, idk
Hyper-V might be fine, im not opposed to Windows at all, but its gonna take a bit to learn how to use Windows. Solaris 11 is also an option but id rather not depend on having an Oracle account, even if its "free", however if its virtualization is actually good i might just use Solaris as my host, especially since it still supports SPARC (i plan on buying a SPARC machine)