“Sysjail is a userland virtualisation system for OSs supporting the systrace library. It runs on OpenBSD, NetBSD and MirOS. The first generation of sysjail is as close to a drop-in replacement for FreeBSD’s jail subsystem as reasonably possible. While sysjail currently behaves as a NetBSD/OpenBSD/MirOS implementation of jail, it also provides additonal auditing and resource-limiting utilities.”
I’ll have to check it out on NetBSD i386. Already, work with xen has meant the porting of netbsd kerneld as dom0 as well as domU. But for small applications, a systrace based jail may be able to get the job done plus I like the system control and logging it provides.