OSSEC

OSSEC is an open-source host-based intrusion detection system (HIDS) designed to provide comprehensive security monitoring and threat detection capabilities. It is said to be suitable for organizations of all sizes, ranging from small businesses to large enterprises. OSSEC is commonly used by IT security professionals, system administrators, security operations centers (SOCs), managed security service providers (MSSPs), and financial institutions to enhance their security posture and effectively detect and respond to security incidents.