systemd-nspawn has been called “chroot on steroids”, but if you think of it as Docker with a slightly different target you wouldn’t be far wrong, either. It can be used to spawn containers on your host, and has a variety of options for configuring the containerized environment through the use of private networking, bind mounts, capability controls, and a variety of other facilities that give you flexible container management. There are many different ways in which it can be used.