Project Spark is pretty, encourages creativity and incorporates Kinect directly. The sandbox/game-creation tool became available for Windows 8.1 users back in December, and today it's entering beta on the Xbox One as well. "Does that mean there's a new, free thing on my Xbox One?" you might be asking. Yes, yes it does. Hot dog!
Project Spark isn't in the XB1 store, so how do you get it? The announcement points to a still-active beta sign-up page, so it seems that interested parties still have a few hoops to jump through before getting in. (If you're already in the Windows 8.1 beta, you're in the XB1 version.) Interestingly, there are already several entries on the store for "Spark Tokens" in 500 token increments ($4.99 equals 500); beta or not, it looks like Microsoft's interested in monetizing Spark from the jump. For the full FAQ on the beta, head right here.
Microsoft Xbox One