Zabbix - Track, record, alert and visualize performance and availability of IT resources
SevOne - SevOne provides network managers with monitoring, troubleshooting, and performance reporting capabilities.
Paessler PRTG - An advanced network monitoring solution to monitor network up/downtime, traffic and usage.
Flowmon - Clever Network Monitoring and Security Solution based on NetFlow, IPFIX and Network Behavior Analysis
Observium - Observium
Nagios Network Analyzer - Nagios Network Analyzer is a netflow analysis, monitoring, and bandwidth utilization software.