One feature of vim is that it can be used in terminals on remote servers without X11 forwarding etc. It has got also a diff tool included which can also act on files at different computers. To diff a local and a remote file one can use vimdiff with the following arguments

vimdiff local_file.txt scp://remotehost//absolute/path/to/file.txt

Mind the two slashes after the host, but there is no relative path option.

Unfortunately this does not work with directories like vimdiff does for local directories.