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.
aerotools-ng provides a C interface for accessing the Aquaero5 USB device by Aqua Computer. It consists of a set of functions for data access and conversion, and a commandline tool using these functions as an example implementation. It also includes utilities for exporting sensor data to SNMP to be used by NMS and other monitoring/graphing tools.
Sagan can alert you when events are occurring in your syslogs that need your attention right away. It can store events into a Snort database, so your IDS/IPS data and log data are in the same place. This enables a single console, like Snorby or BASE, to view not only your IDS/IPS data but your log (syslog, SNMP, etc.) data as well. Sagan will correlate the data for you. It also uses 'Snort-like' rule sets, which means it is compatible with Snort rule set management software. It supports multiple output formats that any network administrator will find useful. Sagan can also stop threats based on log analysis via "Snortsam". This allows Sagan to communicate with various types of network devices (Cisco routers/ASA/etc., Linux iptables, etc).
snmp4zabbix provides a simple SNMP interface to the Zabbix monitoring solution. This lets Zabbix monitor itself using the Simple Network Management Protocol. This is an alternate solution to the Zabbix API for integration, to some extent, with any third party software capable of understanding SNMP.
snmpd-pyagentx provides Python3 bindings for AgentX extension of the snmpd part of the Net-SNMP project. It allows you to tie into snmpd, returning your own values for OIDs or whole OID trees right from the Python code. It consists of a thin C interface for snmp_agent_api(3), provided by net-snmp project libraries, and pure Python logic for handling forwarded requests. The C code is loosely based on the python-agentx project codebase by Bozhin Zafirov.