+ Jails
+ Capsicum [1]
+ Netmap [2]
+ Most performing network stack
+ Resource Management (pretty low memory usage)
+ The userspace tools come with the source (no GNU/Linux duality)
+ Clang/LLVM as default compiler stack
[1] - https://www.freebsd.org/cgi/man.cgi?query=capsicum&sektion=4
[2] - https://www.freebsd.org/cgi/man.cgi?query=netmap&sektion=4
A FreeBSD jail is a like a lightweight virtual machine, and is very similar to a Docker container in Linux (though it has been around for about a decade longer than Docker). It provides isolation for processes etc., but uses less resources than a full virtual machine. It is limited in that it has to be the same operating system as the host.
This is a pretty good overview: https://en.wikipedia.org/wiki/Operating-system-level_virtual...
Processes in the jail will only see network interfaces and other devices that have been explicitly exposed to the jail.
As others have said, it's like a vm with no virtualization overhead. You can set up jails with the entire Freebsd fs hierarchy so it runs like another host with its own users. Note that even the root user in a jail is not the same as the real root user. You can then use pkg to install packages within the jail too.