Below the original information from official BackTrack Linux ( http://www.backtrack-linux.org/backtrack/kali-a-teaser-into-the-future/ ) about Kali Linux :
Originally, BackTrack Linux was developed for our personal use but over the past several years, it has grown in popularity far greater than we ever imagined. We still develop BackTrack for ourselves because we use it every day. However, with growth and a huge user base, we have an obligation to ourselves, our users, and the open source community to create the best distribution we possibly can.
With this in mind, about a year ago a bunch of us at Offensive Security started thinking about the future of BackTrack and brainstormed about the features and functionality we’d like to see in the next and future revisions. One of our main topics of conversation was the option of swapping out our custom development environment for a fully fledged Debian-compliant packaging and repository system.
This seemed like a good idea at the time, but little did we know the world of hurt and pain we were getting ourselves into. This single decision concerning the future path of BackTrack brought with it so much power and flexibility that it has changed the face of our distribution.
What’s happened in the past year? We have been quietly developing the necessary infrastructure and laying the foundation for our newest penetration testing distribution as well as building over 300 Debian compliant packages and swearing in 8 different languages. These changes brought with them an incredible amount of work, research and learning but are also leading us down the path to creating the best, and most flexible, penetration testing distribution we have ever built, dubbed “Kali”.