The latest and greatest version of Networking Test has just been released! This new version adds two new features: port sharing and autosending. The autosending feature lets you put in a delay (measured in seconds) which is then used to time the automatic sending of packets. It's pretty useful! Another feature is the port sharing. In Windows that was default, but in OSX* and Linux you had to request that on your own. Now, Networking Test shouldn't try to lock out other applications that try to access the specified UDP port, which makes it more useful for debugging your own applications.
Head on over to Sourceforge and download the file!
*Qt did say that Unix systems disregard the request for a shared port, but they didn't specify if OSX shared that behavior or not. I know that OSX is based on Unix, but they often aren't lumped together in the same category in the Qt documentation.