Packet Sender

Packet Sender is an open source utility to allow sending and receiving TCP and UDP packets. It also supports TCP connections using SSL, intense traffic generation, HTTP(S) GET/POST requests, and panel generation. It is available for Windows, Mac, and Linux. It is licensed GNU General Public License v2 and is free software. Packet Sender's web site says "It's designed to be very easy to use while still providing enough features for power users to do what they need.".