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Pro Pre-installed on OSX and most Linux distributions
Many *nix systems bundle rsync so there's nothing to install. All you need to do is open up the terminal and start using rsync.
Pro Fast and bandwidth efficient
Only the changed parts of files are synced. For instance, if a long log file increases by just a few lines of text, a small diff will be sent to and saved in the archive. Rsync also compresses data in transit.
Pro Works over SSH
SSH support allows sending files securely over the network by encrypting all communcation.
Pro Free and open source
Licensed under GNU.
Con No official GUI
To use rsync, you have to know your way around the command line.