The best free alternative to LibreNMS is Zabbix, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 25 alternatives to LibreNMS and many of them is free so hopefully you can find a suitable replacement. Other interesting free alternatives to LibreNMS are Nagios (Freemium, Open Source), Spiceworks Help Desk (Free), Icinga (Freemium, Open Source) and PRTG Network Monitor (Freemium).
Gather and analyze accurate statistics and performance metrics, visualize it, get notified about current and potential issues without delay, and take advantage of our time-tested professional development and support.
An advanced network monitoring solution to monitor network up/downtime, traffic and usage. Features include availability, performance, and bandwidth monitoring (SNMP, WMI, packet sniffing, NetFlow), instant alerts, reporting, failover clustering.
Munin is a networked resource monitoring tool that can help analyze resource trends and "what just happened to kill our performance?" problems. It is designed to be very plug and play. A default installation provides a lot of graphs with almost no work.
Checkmk is a monitoring tool of servers, applications, networks, cloud, containers, storage, databases, IoT and more. Checkmk is available as Raw Edition, which is 100% pure open source, and as Enterprise Edition with a lot of additional features.
Observium is an autodiscovering PHP/MySQL/SNMP based network monitoring which includes support for a wide range of network hardware and operating systems including Cisco, Linux, FreeBSD, Juniper, Brocade, Foundry, HP and many more.