Cacti

Cacti is an open-source network graphing tool that collects SNMP data and displays usage or performance metrics. Although primarily for visualization, threshold-based alerts can be set for potential incidents (like bandwidth spikes). A web interface shows device graphs and historical trends. Cacti suits smaller IT shops or network admins wanting a free, self-hosted solution for bandwidth/usage monitoring that can signal potential issues requiring incident response if thresholds are exceeded.