No longer maintained, use Layout Control instead

I'm not really using Atom anymore, but Layout Control has the same functionality this provided plus some other additional stuff.

n-panes package

Sublime Text-like n-column layout shortcuts for atom editor.

Use cmd+alt+[n] (where n is a number) to set the layout to n adjacent vertical panes.

E.g. cmd+alt+3 will create a 3-pane layout.

https://atom.io/packages/n-panes