If you were feeling bad about not having an iPhone 5s and that cool slow-mo feature, you can now get close with a new US$1.99 app called SlowCam. The app records to your iPhone storage, then quickly renders it to your camera roll. Rendering of one video clip can take place while you are recording another. An iPhone 5/5c can capture video at 60 FPS, the new iPhone 5s at 120 FPS, and even the older iPhone 4 captures at 30 FPS. The app requires iOS 7.
To get going, you tap and hold the 'slow motion' button on screen. Taking your finger off the button gives you regular speed, then pressing and holding again slows things down. Great, for example, at recording a high dive from a diving board. Regular speed as the diver climbs the ladder, slow-mo for the dive.
There is a zoom feature, but I stay away from digital zoom like the plague as it kills image quality. You can tap the screen to set exposure and focus together or separately.
I tried the app on my iPhone 5s, and of course the quality looked just like the Apple built-in slow-mo app. On an iPhone 5, the slow-mo looked almost as good, but the frame rate was reduced.
If you are interested in slow motion videos and don't have a 5s, SlowCam will do the trick. It's not going to raise the native frame rate of your iPhone, but it does a nice job of rendering a clean video.
As I said, the app requires iOS 7 and is optimized for the iPhone 5, 5c and 5s. That means to get slow-mo you'll need at least an iPhone 4. Owners with older phones will get no satisfaction.