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.
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.
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.