1. Zabbix– Free
A free network monitoring system that includes great data visualization and raises alerts in the dashboard or sent out by SMS, email, or Slack notification. Install on Ubuntu. Uses SNMP to connect hosts and monitor CPU, RAM, HDD, etc
You can find a complete step by step to Install and configure Zabbix on Ubuntu on this link
2. SolarWinds Network Performance Monitor
Far more than just a simple scanner. Most security issues arise when configurations are changed and SolarWinds NPM identifies these and can automatically resolve many.
Get 30 Day Free Trial, OS: Windows Server
3. Paessler PRTG Network Monitor
A unified monitoring system that covers networks, servers, and applications, virtualizations, and off-site resources.
4. NetCrunch Monitoring Suite
A complete network monitoring platform that includes traffic analysis, log management, server monitoring, and application monitoring.
5. ManageEngine OpManager
An SNMP-based monitoring system that covers LANs, virtualizations, WANs and Cloud-based servers.
6. Nagios XI
Nagios XI is a network monitoring software tool that is marketed towards a wide demographic, who are looking for a low maintenance network monitoring solution.
7. Observium
Offers live network monitoring with integrated alerts in both a paid and free version.
8. Icinga
A clone of Nagios Core that is free to use and installs on Windows and plugins that are written for Nagios.
9. Spiceworks Network Monitor
A free, ad-supported SNMP-based network monitoring system with dashboard, SMS, and email alert notifications.
10. LogicMonitor
Logic Monitor is an excellent SaaS product from the moment you start using it. This SaaS tool automatically discovers devices on the network and starts collecting information right out of the box.
