Zabbix - Track, record, alert and visualize performance and availability of IT resources

Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.

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.

netcat - Netcat is a featured networking utility which reads and writes data across network connections...

Intermapper - Intermapper maps your network topology, giving you a live view of what's happening on your network.

Ettercap - Ettercap is a suite for man in the middle attacks on LAN.