FreeBSD has supported nesting of jails natively since version 8.0, which dates back to 2009. Looking at the jail(8) man page, there is an entire paragraph named Hierarchical Jails that explains the concept of jail hierarchy well. It’s one of the many gems of FreeBSD that, although not widely known or used, is, in my opinion, extremely useful.
BastilleBSD plays a central role in this article, and that’s a project I’ve been hearing a lot about recently. I feel like the various BSDs are currently hitting a stride, and there seems to be a lot of movement from Linux to BSD at the moment.