Falling Sand
Perhaps you’ve already seen this thoroughly addictive game, but if not, check out Falling Sand. There is also a module for the Google Personalized homepage, available through GoogleModules.com. Now you can get distracted every time you open your browser.
The basic idea is that particles of different materials are falling from the sky. You can direct them by creating platforms, mix them for different effects, burn them, and more. There is also a strange bouncy protoplasmic thing that doesn’t like salt. Remember, water puts out fire, fire burns oil and plant, salt kills slug, and sand sinks through water.