What are the new features in Kali Linux according to backtrack.

I used BackTrack 5 OS. I have a small inquiry about the latest version which is the Kali Linux. I wanted to install it but when I checked on the specifications, it says, the new version is based on Ubuntu. For all I know, Kali Linux is based on Debian and it seems very confusing. What are the difference between the two OS? Is it possible to install my old software to Kali Linux?
