I have found that the best tutorial for Mac users is here.
If brew is not installed then get it.
brew cask install virtualbox
brew cask install vagrant
brew install packer
Need to clone the metasploitable3 Github repository.
git clone https://github.com/rapid7/metasploitable3.git
install the vagrant-reload plugin.
vagrant plugin install vagrant-reload
cd metasploitable3
packer build --only=virtualbox-iso ./packer/templates/windows_2008_r2.json
vagrant box add packer/builds/windows_2008_r2_virtualbox_0.1.0.box --name=metasploitable3-win2k8
vagrant up win2k8
And that is really all it takes on Mac.