Xen is a full-fledged hypervisor that hosts VMs. It uses QEMU for I/O emulation in VMs, which increases the attack surface.

Kwarantine is a thin hypervisor that hosts containers. It uses hardware virtualization extensions, MMU, and page tables to provide the same level of security as VMs. Each container runs with a separate copy of the host kernel so that vulnerabilities/bugs are isolated. It does not use QEMU.