It offers several features making it easy to manage Debian package repositories:
- make mirrors of remote Debian/Ubuntu repositories, limiting by components/architectures
- take snapshots of mirrors at any point in time, fixing state of repository at some moment of time
- publish snapshot as Debian repository, ready to be consumed by apt
- controlled update of one or more packages in snapshot from upstream mirror, tracking dependencies
- merge two or more snapshots into one .

This is the main package, it contains the aptly command-line utility.