Fast forward to that scene in a World War II movie where a grizzled, cigar-chomping sergeant removes the dusty tarp covering the Big Guns. That's approximately what it feels like to pick up Kali and start playing around with it.
Kali Linux is the world's most popular offensive-security-optimized Linux distro. Maintained and managed by the fine folks at Offensive Security, Kali was born in 2006 as BackTrack Linux, but after a major refactoring in 2013 got the name Kali. What does the name mean? Well, we'll get to that.
Kali is free to download and use but is intended as a specialized Linux distro optimized for penetration testing and not as a day-to-day operating system for checking your email or web browsing or sharing cat gifs on the Book of Faces.