Several days ago I release Ballistic Energy Calc on the Android Market. It's a free app that calculates muzzle energy and Taylor KO Factor. It isn't especially useful, but it is unique in the fact that it is the only ballistic energy calculator currently available for Android that includes the Taylor KO Factor. I developed and tested it on an Android 2.2 HTC Incredible. The GUI is pretty plain and fairly small, this should hopefully make the app available to users with a wide variety of hardware setups.
Bug: It appears that some users are able to type a space in an input field, despite my best efforts to limit the input using "android:inputType". This results in an IllegalStateException caused by a NumberFormatException. I will be sure to fix this in subsequent releases.
I learned a lot about android by doing this project and I encourge anybody reading this to try developing your own app. After developing the app and testing it for my own phone, I decided that I might as well publish it since somebody else might be looking for something like this. It's actually easy to become a publisher for Android. You just need to pay $25, upload your .apk, and fill out some fields such as the application name. The $25 is a one time fee, so you don't need to pay to publish additional apps. I hope to release some more apps in the future, hopefully of even greater use.