PuTTY - Popular free terminal application. Mostly used as an SSH client.
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.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
tcpdump - tcpdump is a common packet analyzer that runs under the command line.
iTerm2 - A terminal emulator for macOS that does amazing things.
netcat - Netcat is a featured networking utility which reads and writes data across network connections...