CopyMergeForOSX 1.0

You can select a target location and then drag all the files you want to copy into the app and it will tell you which files already exist and will be overwritten. You can then deselect the ones you don`t want to be overwritten or you just go on and merge the folders – replacing the existing files in the target location with the copied ones. The only option seems to be to delete the target folder and replace it completely with new content.