Keryx lets Debian users (that means Ubuntu, too) who don’t have a great Internet connection install new software and keep old software up-to-date.
The problem: Debian software packages typically require a bajillion dependencies. It can be impossible for a human to track down the right files just to install one program on their computer. So smart people have written programs to figure it out for you. But those programs rely on a solid internet connection.
So Keryx takes a snapshot of your computer (a “project” in Keryx terminology) and lets you download the right package files from your favorite Internet cafe. If you’re like I was a few years ago, that’s a coffee shop twenty minutes away.