Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
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.
Fing - Discover which devices are connected to any Wi-Fi network, map devices, detect intruders, assess...
Winsock Packet Editor - WPE Pro is a packet editor.
SoftPerfect Network Scanner - Powerful multipurpose network administration tool for Windows and macOS
Nipper - Nipper - Neat Internet Protocol Packet EditoR - is a graphical packet generation tool.