Thanks to the ubiquitous version that’s bundled with Windows, pretty much everyone has played a few rounds of digital Solitaire. But for Zach Gage, the most popular version of the game was lacking the variety and challenge found in the many real-world iterations of the card game. So two years ago he developed Sage Solitaire, an experience explicitly designed with a smartphone in mind, that fused Solitaire with Poker to add new elements of strategy. Now he’s taking a second shot at making the ideal mobile Solitaire by looking at the game from a slightly different angle. “I wanted to have another go at that design problem,” says Gage.

His new game Flip Flop Solitaire is based on Spider Solitaire, a variant that involves placing cards in 10 stacks, with the goal of converting them into four neat piles, with each card placed in sequential order. Gage describes Spider as “the first Solitaire game that I ever really enjoyed.” (He has a history of innovating in genres he dislikes, which has led to inventive takes on Chess and word games.)

The first thing he did when adapting for mobile was cut the number of piles in half; with only five stacks, it was much more manageable on a smartphone screen. And because the game had half the number of piles, Gage wanted to make each one twice as useful. That led to Flip Flop’s biggest shift. In traditional Spider Solitaire, you can place cards on each other in descending order, so a 6 can be placed on a 7, but not vice versa. But in Flip Flop, they can also be stacked in ascending order. So if you have a stack with an 8,7,6 you can build on it with another 7,8,9 or 7,6,7 or any similar combination. Cards of different suits can be mixed together, though you can only move groups of cards together if they’re all the same suit.

It’s a seemingly minor change that completely alters the way the game works, offering a significant amount of freedom for how you approach things. Instead of uncovering a series of piles and placing them in order, you end up creating a series of messy stacks that you then have to unravel again to put them in order. Gage describes it as a process of “tying and untying knots,” and it can be hard to understand at first. One of the reasons I enjoy Solitaire is because it’s so satisfying to make neat, nicely ordered piles. In Flip Flop, that line of thinking doesn’t get you very far — in order to unravel each pile successfully, you’ll inevitably make a mess, which you’ll eventually have to unravel again.

One of the most interesting aspects of Flip Flop is how it approaches difficulty. The game is divided into a handful of modes, and at the most basic level all cards are the same suit. This eases you into the idea of stacking cards in multiple directions without burdening you with the mess that comes from multiple suits. When you want more of a challenge, you can move to two suits, and it goes all the way up to five. Each mode comes with its own challenges, and forces you to think about the game in a slightly different way.

“I think of it as changing the scope of the problem, as opposed to changing the difficulty,” says Gage. “Suddenly there are all of these other factors that I have to think about all of the time. It’s a different kind of question you’re being asked to solve when you play two suit versus one suit.”

The flexible difficulty was a direct response to Sage Solitaire. While Gage was largely satisfied with how that game turned out — and it was also one of the most commercially successful games he’s ever made — its combination of Solitaire and Poker proved a little too challenging for many players.

“At the time that I made Sage, I really felt like it was one of the most accessible, least punitive games that I had made in a while,” he explains. “But there were a lot of people in comments and reviews who thought that Sage was way too hard, that the challenge level was too high.”

Flip Flop lets you work your way up to that challenge. Each time I’ve added a new suit — I’ve just started playing with four — it’s a struggle at first. The extra constraint forces you to think more carefully about how you move cards around, lest you create a knot that can’t be untied. There’s a hint button, but it only shows you which moves are possible, not which are the best. If I had started out by playing the three or four suit modes I probably would’ve been scared off, because they feel almost impossible the first time you try. But by taking things one step at a time, Flip Flop really ease you into the concept, and when I eventually worked my way up to four suits I felt very comfortable playing.

Flip Flop is also a game that feels great on a touchscreen, even though it also technically works as a physical game with a real deck of cards. The layout is compact in a way that feels right on both a small phone screen and a big iPad Pro. But what the shift to digital really gives you is the freedom to experiment. Because it’s so easy to move cards around, there’s no real barrier to trying out different moves and ideas. Contrast that with a physical deck, where shifting around a stack of 10 cards is a real pain. The same goes for when you get stuck: restarting a game in Flip Flop involves nothing more than tapping a button, as opposed to cleaning up a big mess of cards.

“That may be one of the reasons why Solitaire is so constrained,” says Gage, “because when you un-constrain it it starts to become really unwieldy to play. It’s just a lot more fun digitally.”

As a game designer, that’s the thing that keeps him coming back to Solitaire: it’s not just wildly popular, there are also so many permutations to play around with. That said, even though his next game probably won’t be yet another modern Solitaire variant, it’ll likely be influenced by the card game in some way. “I’m pretty bad at assessing what I will be interested in,” he says, “but it’s very possible I’ll be using some aspect of Solitaire in the future, in a very different game.”

Flip Flop Solitaire is available now in the App Store.