APK Editor is a powerful tool that can edit/hack apk files to do lots of things for fun.
It can help us to do things like string localization background image replacement layout re-architecting and even ad eliminating permission removing etc. What it can do depends on how you use it. However to use it well we need a little bit professional skills. Don't be afraid some examples are given in the help page.
This is the pro version compared to free version here are some extra features:
(1) Support smali code editing
(2) Support app data editing
(3) Support the patch feature
(4) AD free