zchunk is a compressed file format that splits the file into independent chunks. This allows you to only download changed chunks when downloading a new version of the file. Files can hosted on any web server that supports HTTP ranged requests, with no special software required to serve the files (though to download only the changed chunks, your client must be zchunk-aware).

zchunk files are protected with strong checksums to verify that the file you downloaded is, in fact, the file you wanted.