Lynis - Security auditing tool for Linux, macOS, and UNIX-based systems. Assists with compliance testing (HIPAA/ISO27001/PCI DSS) and system hardening. Agentless, and installation optional.

Wazuh - The Open Source Security Platform. Unified XDR and SIEM protection for endpoints and cloud workloads.

API, CLI, and Web App for analyzing and finding a person's profile in 1000 social media \ websites

Prowler is the Open Cloud Security for AWS, Azure, GCP, Kubernetes, M365 and more. As agent-less, it helps for continuous monitoring, security assessments & audits, incident response, compliance, hardening and forensics readiness. Includes CIS, NIST 800, NIST CSF, CISA, FedRAMP, PCI-DSS, GDPR, HIPAA, FFIEC, SOC2, ENS and more

Scapy: the Python-based interactive packet manipulation program & library.

Agent-less vulnerability scanner for Linux, FreeBSD, Container, WordPress, Programming language libraries, Network devices

Adversary Emulation Framework

A curated list of awesome search engines useful during Penetration testing, Vulnerability assessments, Red/Blue Team operations, Bug Bounty and more

List of open source tools for AWS security: defensive, offensive, auditing, DFIR, etc.