Metasploitable 3
VM built from the ground up with many security vulnerabilities for use as a target when testing exploits with Metasploit. Windows 2008 R2 and Ubuntu 14.04 boxes; Vagrant/Packer.
Notes
Prebuilt: vagrant up from app.vagrantup.com/rapid7. Build: 65GB space, 4.5GB RAM; Packer, Vagrant, VirtualBox/libvirt/VMware. ./build.sh windows2008 or ubuntu1404. Login: vagrant/vagrant. Wiki lists vulnerabilities.