An ethical Hacker needs a lot of tools to accurately perform a Penetration Testing on a targeted and authorized network. Please make sure that you are performing Penetration testing on a network that you have the right authorizations to do so. Kali Linux (https://www.kali.org/), Parrot OS Linux (https://parrotlinux.org/), BlackArch Linux (https://www.blackarch.org/) are some of the common Linux distros or distributions that Ethical Hackers use to perform authorized attacks to a network. These distros come with a lot of preinstalled tools that you can run on a virtual machine like VirtualBox (free) or VMware (free version or paid version).
Listed below are some of the tools that often are used to perform a pentesting.
Nmap: (open source) is a security scanner, port scanner, as well as a network exploration tool. It was created by Gordon Lyon also know by his pseudonym Fyodor Vaskovich. Nmap is used by security and systems administrators to assess their own networks for vulnerabilities. If you are interested in reading a book about Nmap, I suggest "Nmap Network Exploration and Security Auditing Cookbook Third Edition by Paulino Calderon - Packt>" (I'm not receiving any compensation from the editor or author of the book). It is available for Linux, Microsoft Windows and Apple OS X.
More info about this powerful tool https://nmap.org/
Aircrack-Ng: (open source) is a series of different tools for evaluating Wi-Fi network security. It is a powerful tool that requires a wireless network interface controller (an external antenna like Alfa works great https://www.alfa.com.tw/) that supports monitoring mode. The software suite includes about 16 different tools like: airmon-ng, airodump-ng and airdecap-ng. The software suite is available for Linux, Microsoft Windows and Apple OS X.
More info https://www.aircrack-ng.org/
Wireshark: (open source) is a packet analyzer and can perform deep inspections of many protocols. It is used for network troubleshooting, analysis, software and communications protocol development. It is very useful when you study for certification like Cisco CCNA 200-301. It's a must have for Ethical Hackers and Network Administrators. The software is available for Linux, Microsoft Windows and Apple OS X.
More info https://www.wireshark.org/
Metasploit: (open source , paid Pro version) is the world's most used penetration testing framework. It was created by H.D. Moore in 2003 as a portable network tool using Perl. Metasploit framework is a tool for developing and executing exploit code against a remote and authorized target machine. Over 2000 exploits are applicable to multiple platforms. "Metasploit The Penetration Tester's Guide by David Kennedy, Jim O'Gorman, Devon Kearns, and Mati Aharoni with foreword by the Metasploit's creator H.D.Moore - No Starch Press" is highly recommended to have in your library.
More info https://www.metasploit.com/