Rock/Paper/Scissors via VNC. Everyone who logs into the server at the same time plays one another every ~15 seconds. With a leaderboard!
Watch out, though—there's no compression, so this can easily use gigabytes of data in just a few minutes!
For help, e-mail tom@alltom.com or contact @alltom on Twitter
I recommend copying the parts you need into your project. I don't consider this module's API stable at all.