Developer website: Joe Workman
The Responsive Layout stacks replace the out-of-the-box 2, 3, 4 and 5 column stacks for responsive-based themes. The columns will break at customizable points so that your content looks good on all browsers from the desktop to the iPhone. There is a 5th stack in this set that will allow you to show or hide content based on the browser size. This allows you to hide content that may not be needed on an iPhone.