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 is some differences:
(1) No function limitation
(2) No ad
(3) Better support
(1) bugs fixes (both for crash and build issue)
(2) support resources extracting
(3) system apps could also be displayed to edit
(4) could edit AndroidManifest.xml in text