Kali is a complete re-build of BackTrack Linux, adhering completely to Debian development standards. All-new infrastructure has been put in place, all tools were reviewed and packaged, and we use Git for our VCS.
More than 300 penetration testing tools: After reviewing every tool that was included in BackTrack, we eliminated a great number of tools that either did not work or had other tools available that provided similar functionality.
Free and always will be: Kali Linux, like its predecessor, is completely free and always will be. You will never, ever have to pay for Kali Linux.
Open source Git tree: We are huge proponents of open source software and our development tree is available for all to see and all sources are available for those who wish to tweak and rebuild packages.
FHS compliant: Kali has been developed to adhere to the Filesystem Hierarchy Standard, allowing all Linux users to easily locate binaries, support files, libraries, etc.
Vast wireless device support: We have built Kali Linux to support as many wireless devices as we possibly can, allowing it to run properly on a wide variety of hardware and making it compatible with numerous USB and other wireless devices.
Here is a complete list of all distributions available.