TrafficMonitor - TrafficMonitor is a network monitoring suspension window software in Windows.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
NetBalancer - NetBalancer is a Windows application for local network traffic control and monitoring.
Datadog - See metrics from all of your apps, tools & services in one place with Datadog's cloud monitoring as a service solution. Try it for free.
FreeMeter - Monitor network bandwidth (C#.NET 2k/XP+). Desktop and Systray graph.
Prometheus - An open-source systems monitoring and alerting toolkit.