Winsock Packet Editor - WPE Pro is a packet editor.

Scapy - Scapy is a powerful interactive packet manipulation program.

Nipper - Nipper - Neat Internet Protocol Packet EditoR - is a graphical packet generation tool.

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.

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.

Pypacker - Pypacker is a fast and simple packet creation and parsing library for Python.