Check_MK is a complex addon for Nagios/Icinga and consists of three subprojects. The check and inventory system Check_MK is a general purpose Nagios plugin for retrieving data. It adopts a new approach for collecting data and obsoletes NRPE, check_by_ssh, NSClient, and check_snmp. It features a significant reduction of CPU use on the Nagios host and automatic inventory of items to be checked, and is especially useful with larger Nagios installations. "MK Livestatus" gives immediate and fast access to live and historic Nagios status data. It's a supported backend for many addons including NagVis, NagiosBP, and Thruk. "Check_MK Multisite" is a feature complete replacement for the Nagios GUI, and uses MK Livestatus as a backend. It is very fast, and supports efficient distributed monitoring.
LibreNMS is an autodiscovering PHP/MySQL-based network monitoring system forked from Observium. It aims to be easy to use and painless to deploy, and to support monitoring of a wide range of devices. Observium's license changed to a modified QPL license in May 2012, then was split into free and commercial versions. The aim of LibreNMS is to continue to create a usable NMS, but with a community focus and GPL licensing.
Observium is an autodiscovering network monitoring system focused primarily on Cisco and Linux networks but includes support for a wide range of network hardware and operating systems. Observium has grown out of a lack of easy to use NMSes. It is intended to provide a more navigable interface to the health and performance of your network. Its design goals include collecting as much historical data about devices as possible, being completely autodiscovered with little or no manual intervention, and having a very intuitive interface.
WapSNMP is an SNMP client library for Go. It allows you to query SNMP servers for any variable, given its OID (no MIB resolution). It has been written to be in the Go style, which means it should be very resistant to all error conditions. It's entirely non-blocking/asynchronous, very fast, and will timeout, not block. It's also surprisingly small and easy to understand. It supports SNMPv2c or lower (not 3, due to its complexity), and supports all methods provided as part of that standard. This library works with OIDs and does not support OID-to-name translation.