What programs exist to find and delete "orphan files" left after deleting an Application? I have transferred my system from Mac to Mac for over 15 years. I have preference files and other plists lurking around in my system for programs I tested years ago. 

Is there a smart program that could point me to these orphan files knowing that the application that created them is not on my system?
If you are willing to use Terminal.app you can use find to identify files/folders which haven't been accessed for a long time.


find ~/Library/Preferences -atime +52w will list all prefences which haven't been accessed in the last 52 weeks. 
find -d ~/Library/Preferences -atime +52w -ok rm '{}' \; will ask whether you want to delete it file by file


and if you don't want to get asked for each file, run

find -d ~/Library/Preferences -atime +52w -delete