apt-cacher is a CGI script which can be used by apt-get to request
downloads of Debian packages (and release files) from the Net. Each
downloaded file is cached into a directory, so subsequent requests for
the same filename are filled from the cache. This is useful when you
have multiple Debian installations to update, particularly if you are
on the end of a slow Internet connection. apt-cacher is easy to
install; you only need to have a local Web server on which you can
place the CGI script and create a directory for the cache.