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.
SmartSniff - SmartSniff is a packet sniffer that capture TCP/IP packets and display them as sequence of conversations between clients and servers.
Ettercap - Ettercap is a suite for man in the middle attacks on LAN.
netcat - Netcat is a featured networking utility which reads and writes data across network connections...
PCAPdroid - PCAPdroid is an android app to capture the phone traffic and analyze it remotely (e.g. via Wireshark). The traffic can be easily downloaded from a remote device thanks to the integrated HTTP server, or streamed to a remote UDP receiver.
Packet Sender - Packet Sender can send and receive UDP, TCP, and SSL on the ports of your choosing.