Let's say I have at home 3 computers running Debian testing. They mostly have the same configuration and most of the packages installed are identical.
Every time I update/upgrade the Debian packages, they are downloaded from the Internet.
Is there a way to pre-fetch the Debian packages from the Internet and have a local, up-to-date Debian repository containing only the packages I have installed that have an available update?
So, typically, if I have vim installed and an update is released, my server will go and fetch the .deb locally and I could upgrade all my machines from the LAN. If I want to install emacs, then the local repository will not have it and it will be downloaded from the Internet.
One could call it a local apt caching system, like Squid does http caching.