• % ssh moria.org.uk
• cph@moria% wget http://www.mirrorservice.org/sites/ftp.x.org/pub/X11R6.8.2/src/X11R6.8.2-src3.tar.gz
• cph@moria% ~/zsync-0.3.1/zsyncmake -b 2048 -u http://www.mirrorservice.org/sites/ftp.x.org/pub/X11R6.8.2/src/X11R6.8.2-src3.tar.gz ./X11R6.8.2-src3.tar.gz
• cph@moria% mv X11R6.8.2-src3.tar.zsync /var/www/zsync/s/
• cph@moria% logout
• % wget http://zsync.moria.org.uk/s/X11R6.8.2-src3.tar.zsync
• % zcat /usr/ports/distfiles/xorg/X11R6.8.1-src3.tar.gz | zsync -i /dev/stdin X11R6.8.2-src3.tar.zsync
• reading seed file /dev/stdin: ****************************************************
• downloading from http://www.mirrorservice.org/sites/ftp.x.org/pub/X11R6.8.2/src/X11R6.8.2-src3.tar.gz:..
• downloading from http://www.mirrorservice.org/sites/ftp.x.org/pub/X11R6.8.2/src/X11R6.8.2-src3.tar.gz:
• hashhit 898738, weakhit 29601, checksummed 42053, stronghit 21757
• verifying download...checksum matches OK
• used 44537856 local, fetched 2389527

10MB download reduced to 0.29MB .zsync file and 2.39MB transfer to update from the previous version. But there are far too many steps here; there's no way this is convenient to use yet. Top of the todo list:

• Automatically recognise compressed local file data.
• rsh/ssh client support