Sounds a bit similar to lftp[1]. While I don't think it supports partial updates or updates of compressed files like zsync, it doesn't rely on a meta-file and also supports a range of other protocols. You can essentially just point it at a website, directory index, ftp server, torrent etc. and it will let you browse the files, create mirrors or update local files.

[1] https://lftp.yar.ru