Kali Linux is an one of the best operating software in the world.
Kali linux is an open source and it is absolutely free for everyone. You can download and use it for hacking.
Kali Linux is a Debian-based Linux distribution aimed at advanced Penetration Testing and Security Auditing.
Kali contains hundred tools which are geared towards various information security tasks, such as Penetration Testing, Security research, Computer Forensics and Reverse Engineering.
Kali Linux is developed, funded and maintained by Offensive Security, a leading information security training company and released on 13th march 2013.
Many hackers use it for penetration testing. Kali contain approx 600 tool which was intresting and we can hack anything with the help of kali linux.
Installation is easy. You can run Kali in virtual machines ( VM ware, virtual box) and run as live in your PC/laptop.
You can also run this on android device but on android, it dont work properly and many tools not work.
Kali is not easy because it is based on commands. So, before starting, you want to learn lots of command to use it.