Game-crafter Project Spark's closed beta on Windows 8.1 starts today, with Microsoft announcing this morning it has begun inviting those who've previously registered on the game's site. The company claims to have had "hundreds of thousands" of sign-ups since the program's announcement at E3.

The beta will begin on Windows 8.1 and was previously reported to begin on Xbox One in January, but is now defined as "early next calendar year." If you're looking for a deeper dive on what Project Spark is exactly, here's 40 minutes of gameplay.
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"Project Spark" Global Beta Begins Today on Windows 8.1
Team Dakota invites players and creators to one the most anticipated next-gen games of this decade

Microsoft and Team Dakota have begun inviting fans and creators who have registered on http://projectspark.com to participate in shaping one of the most anticipated games of 2014 with the "Project Spark" Beta Program exclusively on Windows 8.1.

Since "Project Spark" was announced at E3 in June, hundreds of thousands of fans have signed up for the closed beta, which has begun rolling out today. Starting exclusively on Windows 8.1 and available to fans on Xbox One early next calendar year, registered beta participants are welcomed to a dynamic community where players create and creators play. The beta for both platforms will continue until the product launch next year.

"Project Spark" is an endless adventure where everything is customizable. Jump into an open world sandbox where players can create their own games, movies, stories and more and then share them with family, friends, and the world.

Play what other creators have made and take part in unlimited adventures.
Make games while playing with the revolutionary Crossroads mode.
Bend, shape, and mold worlds with sculpting and beautifying creations with paints and biomes.
Master the easy to use brain system to add behaviors to anything and bring creations to life.

"Project Spark" is the ultimate interactive playground for gamers of all ages, delivered as a free digital download with many options for enhancing your creative experience. It's a powerful gaming destination where creation and play live seamlessly together. Walk in to the community's collective imagination and start playing.

This article was originally published on Joystiq.