PortMapper - Do you need to map a specific TCP or UDP port on your machine to another port on another machine?
iperf - A TCP, UDP, and SCTP network bandwidth measurement tool
netcat - Netcat is a featured networking utility which reads and writes data across network connections...
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...
Komodia Relay - Free open source tool to perform TCP based session relay
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.