When smartphones appeared a decade ago, free-to-play games already existed on Facebook and feature phones. But the App Store was a new, unique market; it would take years for F2P games to become optimized for the platform.

A similar evolution has taken place in ad-based games. When rewarded ads became popular, more developers were able to rely on in-game ads for revenue. But the perfect form of ad-based game didn’t emerge immediately — it had to evolve over years.

Today, the Top Free rankings are full of ad-supported games that are dead simple and undemanding of players, yet more polished than casual games of the past. Here’s a look at four publishers who figured out how to rule the app stores with in-game ads.

Voodoo: Small But Polished Games

France-based Voodoo has been crushing it after scoring a $200 million investment from Goldman Sachs. At the time of this writing, the publisher has two entries in the App Store’s free Top 10, as well as 20% of the games in the Top 50. Helix Jump, their current highest ranking game, shows Voodoo’s formula at its best — one-tap, easy-to-learn controls and rich visual effects.

Like Ketchapp, also based in France, Voodoo sources games from developers around the world. The company recognizes that quantity is important in ad-supported games. Publishing dozens of viral, fast-growing small games is just as good for revenue as spending years on a single huge game — and a safer bet, too.

It’s also important to focus only on the winners. “If a game has low retention, we will kill it. We kill about 19 out of 20 games that we test,” publishing manager Hugo Peyron told Games Analytics.

Gram Games: Masters of Fast-Paced Development

Gram Games describes itself as one of the pioneers of the super casual genre, even before games like Voodoo’s Paper.io exploded on the top free charts. Their breakthrough puzzle game 1010! sits at 179th place in the Top Free charts. Four years after release, players are still tapping away to fill in a simple 10 x 10 grid with colorful blocks.

Although Gram Games has been tinkering with very casual games for years, 2017 was a banner year for them. “In the second half of 2017, we launched four games, compared to the three games we launched in the past few years. So it’s a much quicker pace, with a new game roughly every month and a half,” says co-founder Kaan Karamanci in an interview with GamesIndustry.biz.

Although Gram seems quite different from Voodoo at first glance, the two are similar in one respect: each takes many shots at success, rather than putting all their eggs in one basket. This new way of thinking recently led Zynga to acquire Gram for $250 million.

Rise Up and SuperTapx: Emerging Markets Join the Game

One more important change that ad-supported games have brought to the indie development market is allowing more developers around the world to succeed.

Gram Games has studios in London and Istanbul. Developer Serkan Özyılmaz is based entirely in Turkey and has been a mainstay on the US Top 10 for months with Rise Up, a game in which all players have to do is protect a balloon from falling debris. Chinese developer SuperTapx sits at the top spot of the US App Store with Love Balls, ColorTube, and Draw In. All of these games are controlled using a single motion like swiping or tracing a finger to draw a line.

Throughout the Top Free charts, it’s now possible to find developers who aren’t located in the traditional development hotspots or owned by massive corporations. There are now far more small developers and publishers succeeding around the world with ad-supported games than there are with free-to-play games.