Since moving back to KDE, I've been reacquainted with a lot of my old favourite applications, and perhaps none are as awesome as the KDE Games, KNetWalk in particular. If you've ever played Pipe Dream from the Windows Entertainment Pack days, the gameplay should be a little familiar. Essentially, you're connecting all the chips to the power source.
Insanely addictive. If you're a KDE fan, install KDE Games from your package manager and launch it from the "Tactics and Strategy" menu.