OpenNMS is a free and open-source enterprise grade network monitoring and network management platform. It is developed and supported by a community of user and developers as well as by the The OpenNMS Group, offering commercial services, training and support.
The goal is for OpenNMS to be a truly distributed, scalable management application platform for all aspects of the FCAPS network management model while remaining 100% free and open source. Currently the focus is on Fault and Performance Management.
See live demo:http://demo.opennms.org/opennms/login.jsp
Incinga is enterprise free monitoring system which enables users to follow network and its resources and also notifies them when any problem appear. This tool can monitor as either as complex or large environments across various locations.
Incinga monitoring different network services (SMTP, POP3, HTTP, NNTP, PING…), host resources (CPU load, disk usage…), and many more.
Observium is a PHP / MySQL-based Network Observation and Monitoring System (NOMS) which collects data from devices using SNMP and presents it via a web interface. It makes heavy use of the RRDtool package. Observium has a number of simple core design goals driving its development: minimum interaction, maximum automation and maximum accessibility of information. These design goals have resulted in a slightly unconventional monitoring system with almost no individually customisable settings per device, and where almost everything that can be monitored is automatically discovered.
Project’s homepage: http://www.observium.org/
LibreNMS is an open source auto-discovering network monitoring tool for servers and network hardware. It supports a wide range of network hardware like Cisco, Juniper, Brocade, Foundry, HP and operating systems including Linux and Windows. LibraNMS is a community-based fork of Network monitoring tool “Observium“, released under GPLv3.
LibreNMS is based on AMP (Apache, MySQL, and PHP) / EMP (Nginx, MySQL, and PHP) stack and collects the monitoring metrics via SNMP protocol.
Project’s homepage: https://www.librenms.org/
If you wish to see other tools in this article, please feel free leave a comment here with a brief description of the suggested tools.