rsync
rsync [OPTION...] SRC... [DEST]
rsync is a fast remote file copying tool. It can copy locally or remotely, using either a remote shell or a remote rsync daemon. Its main feature is its delta-transfer mechanism, which only sends the files which differ between the source and destination.
rsync is a great tool for backups or keeping files up-to-date between machines. I find it really handy for uploading HTML and package repositories to web servers.
Examples
Backup your entire home directory
$ rsync -av /home/garry /backup
Publish a web site to a remote host
$ rsync -avz /var/www/shellspells/htdocs webserver:/var/www/shellspells
