Open Source Monitoring System for performance and availability.
This is now also available here github.com/sharkcz/collectl.git
Full-featured enterprise network management tool
FlowViewer is a web-based netflow data analysis tool.
Storage, SAN, LAN Performance Monitoring: IBM,NetApp,Hitachi,HPE,EMC
free netflow analyzer
Monitorix is a system monitoring tool
OPTOSS Next Gen Network Management System (NG-NetMS)
Track your ARP/MAC table changes and so much more