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.
BGPHist is a tool that receives MP-BGP updates, decodes them, and writes them to a database for logging and monitoring purposes. It supports not only Internet routes, but also IPv4 VPN, IPV6 VPN, and L2VPN. It sounds text output, MySQL databases, and Oracle databases. For the MySQL backend, there is also a simple PHP frontend. It could be used to monitor and log an ISP's customer activity for Internet and VPNs, as a passive BGP looking glass, or as a backend for some external monitoring and accounting system.
Sanewall is a firewall builder for Linux that uses an elegant language abstracted to just the right level. This makes it powerful and easy to use, audit, and understand. It allows you to create very readable configurations even for complex stateful firewalls. Sanewall can be used for almost any purpose, including control of any number of internal/external/virtual interfaces, control of any combination of routed traffic, setting up DMZ routers and servers, all kinds of NAT, providing strong protection (flooding, spoofing, etc.), transparent caches, source MAC verification, blacklists, and whitelists. Newer versions abstract the differences between IPv4 and IPv6, allowing you to define a common set of rules for both, while permitting specific rules for each as you need. Sanewall is a fork of FireHOL and can make use of existing FireHOL configurations.