PhoneSaber

Forget all those dumb "flashlight" apps for iPhone: this is the ultimate free gizmo app (and probably one of the few I will bother to review).

First of all, it takes advantage of the platform's accelerometer technology to detect fast or slow accelerations, abrupt stops, and so forth. Anyone designing a game that is meant to take advantage of this kind of user interaction would be well advised to study carefully how PhoneSaber handles it because (a) millions of people will already be familiar with PhoneSaber and (b) PhoneSaber handles it quite well.

Secondly, the sound design is great. It's quite tricky to sync up such rapid movements with just the right sound playing at just the right time, but PhoneSaber does it. Again, game developers: take note. PhoneSaber sets the bar that you'll be expected to meet or exceed.

One might argue that the main PhoneSaber screen is not visually appealing, and I agree it's fairly simple. However, when you're actually using PhoneSaber, e.g. in a duel to the death with your coworkers, running up and down the hall of your corporate offices, you're not looking at the screen. You're listening for the sounds. Another great lesson for game developers: if the user is rapidly shaking the screen around, they won't be able to see much on the screen.