Nmap: the Network Mapper - Free Security Scanner

slackhq/nebula: A scalable overlay networking tool with a focus on performance, simplicity and security (github.com)

wazuh/wazuh: Wazuh - The Open Source Security Platform. Unified XDR and SIEM protection for endpoints and cloud workloads. (github.com)

Zeus-Labs/ZeusCloud: Open Source Cloud Security (github.com)

HackTricks

riramar/Web-Attack-Cheat-Sheet: Web Attack Cheat Sheet (github.com)