tcpdump - tcpdump is a common packet analyzer that runs under the command line.
PortMapper - Do you need to map a specific TCP or UDP port on your machine to another port on another machine?
SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.
netcat - Netcat is a featured networking utility which reads and writes data across network connections...
Komodia Relay - Free open source tool to perform TCP based session relay
Ettercap - Ettercap is a suite for man in the middle attacks on LAN.