NetBSD/xen is a port of NetBSD to the Xen virtual machine monitor. It was first brought to NetBSD by Christian Limpach and committed to the source tree on March 11th, 2004. It is not quite a port in its own right, but an extension to the i386 and amd64 ports. Current versions of Xen also support ARM, but NetBSD has no support for that as of yet.
Xen is a virtual machine monitor for x86 that supports execution of multiple guest operating systems with unprecedented levels of performance and resource isolation. Xen is Open Source software.
For instructions on how to install Xen with NetBSD, see the Xen Howto.
See http://www.xenproject.org/ for more details on Xen.
The current maintainer of NetBSD/xen is Manuel Bouyer.
See also Amazon EC2.