SecurityOnion - Security Onion is a free and open source Linux distribution for intrusion detection, enterprise security monitoring, and log management.
Nessus - Nessus Professional is a security platform designed for businesses who want to protect the security of themselves, their clients, and their customers.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
Tenable.io - Tenable.io Cyber Exposure platform helps to protect any asset on any computing platform and eliminate blind spots.
Suricata - Suricata is a high performance Network IDS, IPS and Network Security Monitoring engine.
AlienVault USM (from AT&T Cybersecurity) - AlienVault USM Anywhere delivers powerful threat detection, incident response, and compliance management for cloud, on-premises, and hybrid environments.