Kali is a Debian-based Linux distribution developed for the purpose of security testing. Having hundreds of penetration testing tools preinstalled, Kali is a ready-to-use OS. We can run it off a live CD, USB media, or in a virtual machine.
The latest versions of Kali have gone through some major changes, one of them being, since Kali 2.0, that the entire system has been shifted to a rolling release model. Now we can simply install Kali 2.0 or a higher version on our system and get the latest versions of the tools in it through normal updates. This means we don't have to remove the existing OS and install the latest version of Kali 2.2 to get the latest stuff.
To explore Kali 2.2, download the latest version of it from its official website at https://www.kali.org/downloads/.
We can download the ISO and then burn it to a CD/DVD or create a bootable USB...