mkjail can be used on FreeBSD to create new jails, keep them updated,
and upgrade to a new release.

mkjail requires the use of ZFS and will create each new jail in a
separate filesystem.

mkjail is not a jail manager.  Jails are configured via /etc/jail.conf
and started/stopped via service jail start foo.

WWW: https://github.com/mkjail/mkjail