I’ve documented the process of installing a Docker Swarm cluster inside VirtualBox with Docker Machine. This allows experimenting with Docker Swarm, the simple docker container orchestrator, over VirtualBox.
This allows you to play with orchestration scenarii without having to install docker on real machines.
Also, such an environment may be handy for teaching if you don’t want to install docker on the lab’s host. Installing the docker engine on Linux hosts for unprivileged users requires some care (refer to docs about securing Docker), as the default configuration may allow learners to easily gain root privileges (which may or not be desired).