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Just go with AppCleaner. It is free and does the same (and sometimes even better) job than AppZapper.

Personally I use AppDelete tho, which costs $7.99, but does an even better job finding those leftover files than the two above-mentioned apps.
 
App Cleaner for me- I liked the clean UI of App Zapper but Cleaner finds more files and the Smartdelete option finds all the associated files if you simply put an App in the Trash.
 
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