Zabbix - Track, record, alert and visualize performance and availability of IT resources
NetSpeedMonitor - NetSpeedMonitor is a lightweight Network Monitoring Toolbar for your Windows Taskbar
Observium - Observium
TrafficMonitor - TrafficMonitor is a network monitoring suspension window software in Windows.
Nagios - Complete monitoring and alerting for servers, switches, applications, and services
GlassWire - Visualize network activity in detail, get notified when new apps access the network, look out for...