iperf - A TCP, UDP, and SCTP network bandwidth measurement tool

Winsock Packet Editor - WPE Pro is a packet editor.

netperf - Netperf is a benchmark that can be used to measure the performance of many different types of networking. It provides tests for both unidirectional throughput, and end-to-end latency. - HewlettPack...

Scapy - Scapy is a powerful interactive packet manipulation program.

jsPerf - A performance playground for JavaScript developers. Easily create and share test cases and run cross-browser benchmarks to find out which code snippet is most efficient.

packeth - packeth is GUI and CLI packet generator tool for ethernet.