PuTTY - Popular free terminal application. Mostly used as an SSH client.
Zabbix - Track, record, alert and visualize performance and availability of IT resources
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
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.
iTerm2 - A terminal emulator for macOS that does amazing things.
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.