Keryx is described as 'Free and open source tool for easily managing packages on offline Debian based computers including support for Ubuntu and Linux Mint' and is an app. There are 2 alternatives to Keryx for Linux and Windows. The best Keryx alternative is APTonCD, which is both free and Open Source.
APTonCD will also allow you to automatically create media with all of your .deb packages located in one specific repository, so that you can install them into your computers without the need for an internet connection.
Sushi, huh? is a program that allows downloading all the packages needed to install the programs you want on GNU/Linux without an Internet connection on your own computer.
