Is there any way to set permissions so that the author is the owner of the file with specific permissions, or are permissions only set by roles over instances or folders?    

I have multiple users that need the ability to upload files into common folders / project areas, but other users should not be able to edit or delete these files, but the author/owner should still have the permission to edit or delete.   

The only way I can see to set security right now is by folder, which forces me to set up separate folders for each user (which is nearly 100), but then folders can't be used to organize files by subject or project and easy viewing.  

Other than separate folders, is there another way to maintain file ownership permissions?

Thank you.
Terence