A GUI that starts up a socket server and displays messages sent to it from connected clients.
This was useful in the early 2000’s for debugging PHP scripts that were either behind a Flash application or generating image outputs. Logging has come along a fair amount since then, but it scratched an itch at the time and was a fun exercise.
Sadly (or fortunately, depending on your perspective), the REALBasic code for the GUI has been lost, but the compiled binaries and the PHP client code is available on Github.