BandwidthD - BandwidthD tracks usage of TCP/IP network subnets and builds html files with graphs to display...
Zabbix - Track, record, alert and visualize performance and availability of IT resources
darkstat - darkstat is a packet sniffer which runs as a background process, captures network traffic...
openITCOCKPIT - openITCOCKPIT is a leading open source monitoring framework based on Naemon (Nagios). In addition it integrates Checkmk and Prometheus. It also offers interfaces to Icinga2, PRTG and opManager to obtain status and performance from them.
vnStat - vnStat is a console-based network traffic monitor for Linux and BSD that keeps a log of network...
Nagios - Complete monitoring and alerting for servers, switches, applications, and services