Winsock Packet Editor - WPE Pro is a packet editor.
iperf - A TCP, UDP, and SCTP network bandwidth measurement tool
Scapy - Scapy is a powerful interactive packet manipulation program.
JPerf - This project gives a better UI and new functionalities to the initial JPerf 1.
packeth - packeth is GUI and CLI packet generator tool for ethernet.
NetStress - NetStress is a user-friendly benchmarking tool that is mostly used by networking professionals to measure the network performance of both wired and wireless connections.