Nmap - Nmap Free Security Scanner, Port Scanner, & Network Exploration Tool. Download open source software for Linux, Windows, UNIX, FreeBSD, etc.
Scapy - Scapy is a powerful interactive packet manipulation program.
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.
Advanced IP Scanner - Advanced IP Scanner shows all network devices, gives you access to shared folders, and can even remotely switch computers off. Download it Free.
Nipper - Nipper - Neat Internet Protocol Packet EditoR - is a graphical packet generation tool.