- **KVM** works exclusively with QEMU and performs hardware acceleration for x86 VMs with Intel and AMD CPUs. KVM and QEMU are hypervisors that emulate the VMs; the pair is often called KVM-QEMU or just KVM.
- **QEMU** is a machine emulator that can allow the host machine to emulate the CPU architecture of the guest machine. Because QEMU does not provide hardware acceleration, it works well with KVM.
- **libvirt** provides an abstraction language to define and launch VMs, but is normally used just to launch single VMs. It uses XML to represent and define the VM.