Scapy - Scapy is a powerful interactive packet manipulation program.
Wireless Network Watcher - scans your wireless network and displays the list of all computers and devices that are currently connected to your network.
Winsock Packet Editor - WPE Pro is a packet editor.
Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
packeth - packeth is GUI and CLI packet generator tool for ethernet.
Angry IP Scanner - Open-source and cross-platform network scanner designed to be fast and simple to use