What exactly is Kali Linux?
Kali Linux (previously called BackTrack) is a free, open source, Debian-based Linux distribution. This operating system has hundreds of applications installed, which can help us to conduct a successful penetration test.
And, guess what? Kali Linux is used by bad hackers (also known as black hat hackers), too. This means that we (security professionals) will have more accurate results, because we are using the same tools that the bad guys use to compromise systems.
You can install this beast on any virtualization host (VMware, VirtualBox, or HyperV). Also, you can install it on an ARM processor-based computer, like the Raspberry Pi.
Finally, you need to know that Kali Linux is developed, funded, and maintained by Offensive Security, and you can visit their site at https://www.Kali.org.