Hiding away in the App Store of the console, once downloaded, you'll be able to put in information about your height and weight, which the games in question will then apparently use in order to track your calories better. Working as a dual fitness hub and assistant, the PlayFit app will be where you head if you want to check how many calories you're burning through while playing Kinect games. Tracking the total you've burnt today, overall, and your average per session, it also ranks you with people from all over the world, letting you see how many calories you've burnt compared to players worldwide, or those on your friends list. Rounding out the cool features list is the ability to earn achievements for hitting certain milestones, such as burning through a certain number of calories overall, or in a single session.
Sadly, the number of games the app currently supports is pretty limited, with it tracking a mere ten games out of Kinect's back catalogue, including some rather odd ones. Of course, Kinect Sports and Dance Central aren't supported in favour of their sequels, to encourage you to upgrade, but the energy burning (and brilliant) Rabbids: Alive and Kicking has been shunned, apparently in favour of the docile Sesame Street: Once Upon a Monster.
Either way, we'll remain hopeful that more games (and older games) will be added as time goes on - it seems something of an odd decision to not support older Microsoft games in the first place, although we can certainly understand the motives. To get started for yourself, head over the Apps section of your console, visit the app marketplace, and set the 100+mb bundle to download. You don't need the Kinect sensor in order to browse the app, so even if you don't have Kinect, why not give it a look, and see what you're missing out on?