Tails is a live operating system built on Debian that uses Tor for all its internet traffic. Its main goal is to give you security through anonymity.
With it, you can browse the web anonymously through encrypted connections.
Built on Debian and maintained by Offensive Security Ltd. With around 300 tools for testing the security of a network.
Kali's main focus is on pen testing, which means it's great for poking around for security holds in your own network.
BackBOx is Ubuntu-based distribution developed to perform penetration tests and security assessments. It is designed to be fast and easy to use.
It provides a minimal yet complete desktop environment, thanks to its own software repositories, which are always updated to the latest stable versions of the most often used and best-known ethical hacking tools.