This can be activated from the Packages menu, command palette, from the context menu on the root project folder in tree view, or the git branch indicator in the status bar. A modifier key can also be set to work here on click.
An instance of GitKraken will be spawned for each project by default, but can be configured in the package settings to only ever run a single instance of the application.
apm install gitkraken or search “kraken” under packages within Atom.
Good catch. Let us know what about this package looks wrong to you, and we'll investigate right away.