If you own a Kinect, there's no cost barrier between you and a raucous Kinect Party. Double Fine's latest motion controlled minigame collection will be free upon its December 18 launch, and will stay that way throughout 2012. The regular price is currently unannounced, but it'll be more than nothing.
You can see the kind of augmented realities you and your friends will be entering in this new trailer. You do have to bring your own friends, however: Double Fine isn't supplying those for free.