Ubuntu Linux

The official Atom page lets you download .deb and .rpm packages for Linux, but there's no mention of an official repository you could use so you get automatic updates with each Atom release.

LinuxUprising explains that there are, in fact, official Atom repositories for some Linux distributions, like Ubuntu, Debian, Fedora, Red Hat, CentOS, and openSUSE. Despite most websites recommending third-party repositories, this is the official Atom repository!