PuTTY - Popular free terminal application. Mostly used as an SSH client.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
MobaXterm - Enhanced terminal for Windows with X11 server, tabbed SSH client, network tools and much more
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use
iTerm2 - A terminal emulator for macOS that does amazing things.
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...