iPhone 4S (Jailbroken): The voice-assistant Siri is pretty useful on the iPhone 4S, but there are a lot of things you still can't do with it. This Cydia tweak will cross a few items off that list, including turning on or off wireless settings, setting your screen brightness and reading your battery level back to you.
What's interesting is the way that the developer set up these features. Instead of going to a third-party server to enable it, he can just use a framework to keep these commands local to your phone, which is a plus for privacy reasons. You'll have to jailbreak your phone, just like with all other Cydia tweaks, but if you've already done it, this is a pretty cool addition.