We don't have any all-in-one utilities to manage jails. Just the basic jls, jexec, and jail utilities. The jail(8) manual page should be mostly up-to-date with recent changes to improve options management.
MD is very, very old. Ancient, really. It was removed ages ago because it was old, crufty, and didn't work as well as VN or TMPFS. It basically formatted a UFS filesystem backed by ram. You can use the VN device if you need a block device backed by ram or swap, or the TMPFS filesystem if you just need a ram and swap backed temporary filesystem. We can't bring MD back, sorry. -Matt
