The Open Source Soundboard App for Android
From your Android device, go to http://ninjabit.neocities.org/projects.html and click "Esbee". Your device will automatically download the app and install.
Your device may throw a warning, asking for permission about downloading from Unknown Sources. Temporarily disable it so that Esbee could be downloaded, then re-enable it.
Fork!
You'll need the Android SDK to make code changes. However, you don't need an Android device; an Android device emulator comes with the SDK.
If you have any bugs, suggestions, or ideas, just create an issue. =)