Stack AR was launched last year for iOS and Android. But with iOS 11 rolling out to iPhones everywhere, developer Ketchapp Games rereleased the game with augmented reality. Called Stack AR, it reached No. 1 on the Apple App Store. In the free-to-play games category over the weekend, according to market analyst Sensor Tower. It’s the first game built with ARKit to do so. “Stack was actually one of the best game concepts in the Ketchapp portfolio that we could port into Augmented Reality since the game is about stacking bricks,” said Ketchapp co-director Antoine Morcos in an email. “Augmented Reality brings a new dimension.”

Apple’s First AR Kit game Stack AR to Top Apple’s Free to Play

The rules are simple: As colorful blocks drift to and fro, you have to tap to stack them into a tower. If you’re not exact, part of the block gets lopped off, leaving you with ever-diminishing blocks that get smaller and harder to land. When viewed through Augmented Reality, the tower pops up on any flat surface and casts a shadow. Lending it a sense of physical presence.

It’s still early days for Augmented Reality, though a handful of apps and games have started experimenting with it already. It features 4K effects. Other titles, like Climax Studios’s ARise, aim to take advantage of how AR can enable players to walk around and view the game from different vantage points.

Meanwhile, Morcos says that Stack AR’s simplicity is the reason why it appeals to players and reached the top of the chart.“The first AR games on iPhone must be simple and quickly understandable, otherwise, AR will never go mainstream,” said Morcos. “That is what we think. Our goal is to bring people, especially children, to enjoy AR, and the best way is to keep it simple.”