A really great yet unknown feature that you can use with VirtualBox is the ability to take a screenshot of a running guest system. By using the VBoxManage controlvm command-line utility (see https://www.virtualbox.org/manual/ch08.html#vboxmanage-controlvm for more) of VirtualBox you can do this very quickly and easily.
I’m using an Ubuntu host machine, however I believe you can do the same with MAC or Windows hosts. For example I have a VM guest named stingray and I want to take a screenshot of the current state and screen of the guest machine – to do so I run the following command from my host Ubuntu computer:
vboxmanage controlvm stingray screenshotpng stingrayscreen.png
Now I should have an image named stingrayscreen.png in the path area that I ran the above command!