There are quite a few out there including a few command line ones.
I need software that can scan 2 drives, compare the files and copy the missing ones from each to the other.
This is so I can continually back-up my ever-changing 2 external drives of photographic images. The software needs to be able to assign new file names when necessary, rather than replacing existing files with an updated file of the same name.
I use Windows XP, sp3.