BLËSK - BLËSK is a suite of applications for network monitoring and management.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
SolarWinds Log Analyzer - SolarWinds Log Analyzer tool provides comprehensive log management and analysis with out-of-the-box visibility into performance and availability. Free trial!
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.
Paessler PRTG - An advanced network monitoring solution to monitor network up/downtime, traffic and usage.
FastNetMon - FastNetMon is a very fast DDoS analyzer with sflow/netflow/mirror support.