Android: Android's Four buttons across the bottom have some nice functionality, but aren't super customisable. Clutch Pad adds a small button to the side of your screen that lets you perform a number of useful actions with simple swipe gestures.
Android has some pretty cool actions built into its capacitive buttons (holding search, for example, lets you search by voice; holding home shows you recently used apps), but if you'd like more than what they have to offer, Clutch Pad adds quite a few more actions that you can use. Clutch Pad overlays a very small, transparent semicircle to the side of your screen (which you can show or hide at will) that you can press or swipe up, down, left and right on to perform actions. You can view recently used apps, open your last used app with a quick swipe, go back to the home launcher, or even view a list of favourite apps. It essentially makes navigating apps on your Android phone a lot quicker, and without the need to return to the home screen or open the app drawer.
Clutch Pad is a $2.05 download for Android devices.