Sway is the latest addition to Microsoft's wide range of product line. Announced back this month, it is currently available in a preview version. You'll need to request an invite at the Sway.com website if you're interested in trying out the preview. Except today, you have a chance to join without waiting for that invitation.
It is in invitation only for now. But Microsoft has opened it for a limited time, sign-up for Sway here.
Source: Twitter (@sway)