NetTraffic -
Live data rate chart. Network usage history (statistics). Quota counter (limit usage meter). Works with every network connection. Multi-language. Installer & portable. Lightweight. Freeware.
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Paessler PRTG Network Monitor -
Comprehensive monitoring solution with over 200 sensor types, user-friendly interface, and powerful capabilities such as traffic analysis, failover clustering, and remote probes. Offers email and SMS alerts, supports SNMP and WMI, provides high-availability features and detailed reporting.