Can Hazel do this ? How?

Corlin here:

Here is what I would like to do in more detail.
I have a huge store of old text files. In many different formats. Many of which are duplicates with the only difference being the extension.

1. I want to keep all the files that have extension ".yyy"
2. If two or more files have exactly the same name, and none have extension ".yyy" keep the one that has extension ".zzz"
3. Move the rest to a folder to be checked before trashing.

So how do I make this rule?

I think you'd need to do a script for this. The logic seems very specific in this case. You can now use scripts in conditions so at least that part should be easier.

Corlin here:

Thank you for your prompt reply.

I thought as much. Great chance to get my Apple Script chops back up to speed.

(would you like me to post the script, when I see that it works?)

Sure, if you think other people might be interested in it. The Tips forum is the place for that type of thing.