Nagios® is a comprehensive and fully featured host and service network problem monitoring system.
Net-Policy is a scalable role-and-policy based network management system.
JFFNMS is a Network Management System designed to mantain a IP/SNMP/Syslog/ Tacacs+ Network but can also be used to monitor any standards compliant SNMP device, Server, TCP port, or Custom Poller. Supports some Cisco routers/switches.
NMOPS (Network Management OPerationS) provides standards based networking tools for Service Providers using the Open Source and Free Software model.
Sysmon is a high performance, accurate network monitoring tool.
Mars is a services-oriented network status monitor. It simulates client connections to Internet services and reports when those services are not responding.
PIKT® is a cross-categorical toolkit for monitoring and configuring systems, organizing system security, formatting documents, assisting command-line work, and performing other common systems administration tasks.
Hyperic is an enterprise grade open source monitoring system built from the ground up with Java.
Zenoss is an enterprise-grade open source monitoring platform. Zenoss products provide application, server, and network management capabilities built on the python-based Zope application server.
Groundwork Open Source combines all the advantages of open source software with superior functionality, documentation, and professional support to give you unprecedented visibility and control of your entire IT infrastructure.
OpenNMS is a project that attempts to replicate an enterprise grade Network Management System (NMS) like HP OpenView. The software provides network and system monitoring, trouble ticketing, asset management and rudimentary network mapping.