I would like to know if there is a (free) tool to compare local files with a distant repository. Something with a good gui would be great.
If you add the FTP directory as a Network Place, it can be treated as a local drive.
This means that any directory compare tool can be used, of which there are heaps.
If you need more info, alert me by adding a comment below.
Total Commander is not free but can be evaluated for some times.
You can compare local files with files stored on a FTP site. The "Synchronize Dirs" feature is great at that, comparing directories recursively. For files with differences, you can compare easily their content (if they're text-based).
As explained in this review: