Zabbix - Track, record, alert and visualize performance and availability of IT resources
Nfsen - NfSen is a graphical web based front end for the nfdump netflow tools that allows you to:
FastNetMon - FastNetMon is a very fast DDoS analyzer with sflow/netflow/mirror support.
Andrisoft WanGuard - DDoS protection software solution for networks. Attacks detected by NetFlow,NetStream,sFlow,jFlow,IPFIX,Port Mirroring and mitigated with firewall filters
Abusix - Abusix is a network security company that offers email threat protection and network abuse handling solutions to ISPs, Telcos, and Cloud/Hosting Providers to stop the rapidly growing problem of email-borne threats and other kinds of network abuse.
LibreNMS - A fully featured network monitoring system that provides a wealth of features and device support.