zsync is a file transfer program that allows you to synchronize a local file with a remote server version. zsync is very efficient as it only downloads new parts of the file, using the same algorithm as rsync.
Server usage
Use zsyncmake to build a control file for zsync client, like this:
zsyncmake -z myiso.isoClient usage
zsync http://foobar.com/daily-live/current/myiso.iso.zsync