nmap - Nmap ("Network Mapper") is a free and open source utility for network discovery and security auditing nmap.org
nc - tcp/udp networking utility for reading and writing to network connections netcat wiki
john - John the Ripper is an Open Source password security auditing and password recovery tool
gobuster - Gobuster is a high-performance directory/file, DNS and virtual host brute-forcing tool written in Go. gobuster
Be very careful with default wordlists; example is swagger-ui endpoints
mosquitto - Eclipse Mosquitto is an open source (EPL/EDL licensed) message broker that implements the MQTT protocol versions 5.0, 3.1.1 and 3.1. (https://mosquitto.org/)
snmpwalk - snmpwalk is a command-line utility that uses the Simple Network Management Protocol (SNMP) to query a network device and retrieve a large amount of information, such as details about its configuration, status, and performance (https://linux.die.net/man/1/snmpwalk)
scripting lang - php, python, bash, ...
ldapsearch - Process one or more searches in an LDAP directory server. (https://docs.ldap.com/ldap-sdk/docs/tool-usages/ldapsearch.html)
wireshark/tshark - Comprehensive Network Analysis. Wireshark is a powerful, open-source network protocol analyzer that allows users to capture and interactively browse the traffic. TShark is command-line version of wireshark.
strings - The strings command in Linux is a utility that extracts human-readable text strings from binary files. (https://linux.die.net/man/1/strings)
volatility3 - Tool which can be used to restore file system using OS image with symbols. (https://volatility3.readthedocs.io/en/latest/symbol-tables.html)
curl - Command-line tool for transferring data with URLs. Supports HTTP, HTTPS, FTP and many more protocols. (https://curl.se/)
hashcat - Advanced password recovery tool supporting GPU acceleration and hundreds of hash types. (https://hashcat.net/hashcat/)
impacket - Collection of Python classes for working with network protocols (Kerberos, SMB, MSRPC, NTLM). (https://github.com/fortra/impacket)
rpcclient - Tool for executing MS-RPC functions on remote Windows systems via SMB. Part of the Samba suite. (https://www.samba.org/samba/docs/current/man-html/rpcclient.1.html)
qrencode - Command-line utility to encode data into QR Code symbols. (https://fukuchi.org/works/qrencode/)
docker - Platform for building, running, and managing containerized applications. (https://www.docker.com/)
postfix - Free and open-source mail transfer agent (MTA) that routes and delivers email via SMTP. (https://www.postfix.org/)