SAN FRANCISCO — Crossy Road developers Andy Sum and Matt Hall never set out to rake in a pile of cash. They did, however, want to create a popular game.

“We wanted to make the next Flappy Bird,” said Sum at the duo’s Game Developers Conference session here Tuesday.

“But our goal wasn’t to make money,” added Hall.

And yet make money they did. While Crossy Road hasn’t hit Flappy Bird levels of success (or notoriety), it pulled in 50 million downloads — on iOS, Android and Amazon — during the game’s first 90 days. It also generated $10 million for Hipster Whale, Sum and Hall’s development company.

Not bad for a game that was originally named Roadkill Simulator 2014.

The rapid rise of such a simple game is the type of overnight success story that drives indie developers to keep pounding away at their keyboards in the face of seemingly impossible odds. Explosive growth in iOS and Android game sales stole the market from portable game consoles in 2014, but the sheer number of titles available makes it difficult for developers to rise above the noise.

For Hipster Whale, the Crossy Road secret sauce consisted of classic gameplay, cuddly retro characters — and a whole lot of luck.

Crossy Road plays like a version of ’80s arcade mainstay Frogger, with updated 3-D graphics and wacky characters in place of the vintage game’s log-hopping amphibian. In the new game, a pixel-art chicken has to cross the road, dodging obstacles like cars and predators, to get to the other side. It’s an “easy to learn but hard to master” tap-and-swipe game that is instantly engaging. (You can see it in action in the trailer below.)

The original plan, said Sum, was to make a game in six weeks, which would let the small team get back to other gaming projects.

They both live in Australia, about two hours apart. They collaborated over Skype to design and implement the game. Hall did most of the infrastructure and user interface programming, while Sum did most of the character and sound design. They turned to artist Ben Weatherall for the cubelike design, called voxel (three-dimensional pixels) art.

Sum and Hall looked at Flappy Bird’s addictive qualities and tried to make a game that would engage players, keep them coming back and also have a decent shot at going viral. They didn’t want to have to buy advertising, which requires large outlays of cash. They also didn’t want to add any now-standard free-to-play game tactics like coin packs or energy mechanics (which force you to wait to play or pay to get back in action).

They settled on launching with 50 characters that players could buy to play the game, and video ads, an idea inspired by another hit indie game, Disco Zoo.

“We thought engagement was the most important thing,” said Hall, referring to the advertising, which doesn’t pull players out of the game experience. A majority of items in the game can be acquired by players for free — it’s a fun game and players love to share it with their friends. You can’t buy virtual currency and all the characters play the same (there are no super-powered characters). There’s no mechanic to continue a failed level, and no energy system.

The game, with its quirky, meme-inspired character design, proved to be a big hit, but it wasn’t until ridiculously popular YouTubers PewDiePie and Lonnie Dos started playing the game in their videos that Crossy Road took off like a rocket.

One video star, Amazing Phil, suggested an “emo goose” as a character, driving even more gamers to check out the indie title.

Crossy Road launched just before the holidays in November 2014, and they hit $6.4 million in revenue by the following February. They’ve made $10 million from advertising, in-app purchases, and an incredible number of downloads. They’re happy to get the money, for sure, but they still want to help other developers realize their own dreams.

“Please innovate in your own free-to-play games,” Hall called out at the end of the talk. “Focus on retention, engagement and virality. Innovate the rest.”