Zabbix - Track, record, alert and visualize performance and availability of IT resources
NetVizura NetFlow Analyzer - NetFlow Analyzer is a solution for bandwidth monitoring and traffic analysis. It helps with traffic investigation, analysis and reporting
nfsen-ng - nfsen-ng aims to be an in-place replacement for the ageing nfsen.
Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.
FastNetMon - FastNetMon is a very fast DDoS analyzer with sflow/netflow/mirror support.
Easy-IP - IPAM and DNS for Telecoms