net/zsync 0.6.2nb1 NetBSD

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.