Duplicate file finders are a dime-a-dozen: how about a "non duplicate" file finder?
The gist is: Given two (or more???) folders. Scan the folders and identify those files that are in one folder or the other, but not both. Generate a list. Ideally some mechanism would then allow the selective transfer/copy of those files from the folder which contains them to the folder that doesn't or optionally to another specified folder. A file pattern mask might also be useful. subdirectory recursion, too.
This is one of those program ideas for which the requiremets are obvious when I need to have it, but, I'm not reallly sure I can identify, at this moment,all the uses for this (beyond standard synchonization of folders that is) I'll post more when it comes to me...