Docker has stormed into software development in recent years. While its concepts are powerful and valuable, similar tools have been used in systems for decades. FreeBSD's jails in one of those tools which build upon even older chroot(2). To put it shortly, with these tools, you can make a safe environment separated from the rest of the system.
Jails in FreeBSD are by no means a new tool (introduced in 4.x), but for a reason or another, I haven't used them that often, which is a shame since they are so powerful. So I wanted to explore this concept in a concise and summarized manner.
Source: FreeBSD jails for fun and profit, an article by Topi Kettunen.