zsync is a file transfer program.  It allows you to download a file
from a remote server, where you have a copy of an older version of the
file on your computer already.  zsync downloads only the new parts of
the file.  It uses the same algorithm as rsync.  However, zsync is
designed for file distribution, with one file on a server to be
distributed to thousands of downloaders.  zsync requires no special
server software - just a web server to host the files - and imposes no
extra load on the server, making it ideal for large scale file
distribution.

	Client-side rsync - zsync runs on the client side, thus
	avoiding the high server load associated with rsync.

	Rsync over HTTP - zsync provides transfers that are nearly as
	efficient as rsync -z or cvsup, without the need to run a
	special server application.  All that is needed is an
	HTTP/1.1-compliant web server, so it works through firewalls
	and on shared hosting accounts.

	Handling for compressed files - rsync is ineffective on
	compressed files, unless they are compressed with a patched
	version of gzip.  zsync has special handling for gzipped
	files, which enables update transfers of files which are
	distributed in compressed form.