Mounting a host folder in WSL or VirtualBox Kali machine

Most people using kali won't use it on a dedicated machine. For Windows users most would use kali from WSL (Windows Subsystem for Linux). Other would use a virtual machine in VirtualBox or other virtualization environment. In this post we will only cover VirtualBox.
In this case it can be useful to have a folder on the host machine that can be shared in the kali environment.

case environment folder host kali linux machine people subsystem virtual virtualbox virtualization virtual machine windows wsl