zsync is a implementation of rsync over HTTP. It allows updating of files from
a remote Web server without requiring a full download or a special remote
server application. It uses a metafile, which is created on the server,
to determine which parts of a file the user already has; it then downloads
the remaining parts via HTTP. No special server or Web server module is
needed. It also works with gzip files, and content on the server can be
compressed to further reduce download times.