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.
The library is available as 32-bit and 64-bit: