OpenNMS Horizon

Observium

Observium is a network monitoring platform that automatically discovers devices and services on a network and collects real-time and historical performance data, presenting it through a web-based dashboard. It supports over 450 device operating systems and vendors, including Cisco, Juniper, HP, Dell, Windows, and Linux, and provides threshold, state, and syslog-based alerting. Beyond monitoring, Observium includes traffic accounting and billing features, rule-based automatic device grouping, network mapping, and a RESTful API for integrating with other tools. It ships in a free Community edition, alongside paid Professional and Enterprise editions that add real-time SVN updates and support hours, and is used by organizations including Twitch, eBay, and Spotify.

LibreNMS

LibreNMS is a free, open-source network monitoring system that automatically discovers devices across a network using protocols like CDP, LLDP, OSPF, BGP, SNMP, and ARP, then continuously polls them for health and performance data. It's built to scale horizontally through distributed polling, which lets it handle networks ranging from a handful of switches to large, geographically distributed infrastructure. Alerting is highly configurable and can notify via email, IRC, Slack, and other channels, and the platform ships a full API for pulling monitoring data into other systems or dashboards. It integrates with tools like NfSen, collectd, SmokePing, RANCID, and Oxidized for flow analysis and configuration backup, and includes optional bandwidth billing based on port usage, making it a common choice for ISPs and network administrators who want a self-hosted alternative to commercial NMS products.

Nagios Core

Nagios Core is a free, open-source monitoring solution used to track the health of servers, network infrastructure, and services. It monitors CPU, memory, disk usage, and running processes on Linux, Windows, and Unix systems, along with network devices like switches, routers, firewalls, and load balancers, and services such as DNS, DHCP, FTP, SSH, email, and databases. As the original engine behind the broader Nagios monitoring ecosystem, Core is extensible through thousands of community-developed plugins and integrations, letting it monitor almost anything with a status that can be checked. It's distributed under the GPL v2 license with full source code available on GitHub, and runs on major Linux distributions including Ubuntu, CentOS, Debian, and RHEL.

Zabbix

Zabbix is a powerful open‑source monitoring platform that provides real‑time visibility into the performance and availability of IT infrastructure, applications, and services. It combines a flexible data collection engine with a rich web‑based UI for dashboards, reporting, and alerting. Designed for large‑scale environments, Zabbix supports agent‑based and agentless monitoring, customizable templates, and extensive integration options, making it suitable for enterprises, service providers, and complex hybrid clouds.