It all starts with a circle. The very first level in Hundreds, a new puzzle game for the iPhone and iPad that launches today for a promotional price of $2.99, contains nothing more than a grey circle with the number zero in the middle. You aren't given any instructions. But when you touch it, the number starts to increase, and the circle grows. Once it reaches 100 you've beat the level. It's a simple and natural way to introduce players to the game's central goal — in each stage, all of the circles must add up to 100 before you can move on. And it's a perfect example of Hundreds' focus on minimalist design. There are no tutorials because the controls are intuitive enough to understand just by experimenting. Even the game's title screen is little more than a white circle on a red background. But in spite of this simplicity, or perhaps because of it, Hundreds is an addictive and challenging puzzle game that can stand up to the best iOS has to offer.

Of course, things get a bit more complex once you get past that very first level. When you touch a circle not only does it start to grow, but it will turn red for as long as you hold your finger on it, and if it touches anything while red you'll have to start over. Again, it sounds simple and is easy to grasp, but when you throw in additional challenges like spinning saw blades, circles that can only grow in parallel, circles with negative numbers, and all kinds of barriers to get in your way (or help you out), the challenge ramps up quickly. As with that initial level, almost none of these elements are explained to you in words, but instead a combination of experimentation and subtle visual clues will let you know that bubbles can be popped with a quick tap, or that you can move an obstacle with your finger. These elements help make the basic premise feel consistently compelling over the course of 100 levels.

Hundreds was developed by Semi Secret Software, and is the result of a collaboration between a few notable developers from the iOS gaming community. Adam Saltsman, best known for Canabalt, did much of the design work, while Greg Wohlwend — who previously worked on games like Gasketball and Solipskier — created the art and interface (as well as the amazing website). Meanwhile, Semi Secret's Eric Johnson served as programmer and musician Scott "Loscil" Morgan created the game's ambient score. Hundreds has been in the works since mid-2011 and started life as a Flash prototype, though the initial goal wasn't necessarily to bring yet another puzzle game to iOS. "With Hundreds I just really wanted to help build a great touch screen game," says Saltsman. "It just ended up being a puzzle game."

Saltsman's experience with the one-button hit Canabalt also taught him that sometimes simple is better, hence the strong minimalist tone found throughout Hundreds. "I may yet be proved wrong, but I think over-burdening a design with unnecessary stuff can be a huge distraction to people that aren't used to that sort of thing," he says. "When you cut away the fat, frequently annoying things like tutorials or whatever can be cut away too." At least in the case of Hundreds, this theory proves correct — at no point did I find myself unable to figure out what to do or how a particular mechanic worked. It all just clicked.

On a platform that has provided an embarrassment of riches when it comes to terrific puzzle games — Drop7, Edge, and Triple Town, to name a few — Hundreds clearly has its work cut out for it trying to stand out. But this isn't something the team seems all that worried about. "Hundreds has issues, to be fair, but I don't think standing out is one of them," says Saltsman. "Our goal was just to make the most pure touch screen-based game we could — no 'transmedia synergy,' no filler levels, no IAP, no microtransactions. I think the result is kind of naturally something that doesn't have a lot in common with most puzzle games on the App Store." The game may see some additional content updates in the future, and Saltsman says that he "really, really, really" wants to bring Hundreds to Android at some point.

Based on the name and the goal of each stage, Hundreds may seem like a game fixated on numbers, but the creators don't necessarily see it that way. Instead, they view it as a game about "spatial relationships, the principle of conservation, and even a little entropy." "Take away the numbers," explains Wohlwend, "and the game would play exactly the same." It's really a game about circles, and how they interact with one another within the rules of the game. Yes, it may just be circles. "But then again," Saltsman pointed out, "Tetris is just squares."