Epic is now enabling people to take Fortnite with them wherever they go, and players are rewarding the developer with massive quantities of cash. The last-player-standing shooter launched last week as part of an invite-only program, and it is already the No. 2 highest-grossing iPhone game in the United States, according to data-tracking firm Apptopia. Fortnite is behind only Candy Crush Saga. Games at the top of the iOS charts make an estimated $3 million-to-$8 million per day, so that explains why everyone looks cooler than me in Fortnite.

Fortnite is one of the most popular games in the world right now thanks to its free-to-play Battle Royale mode. Like PlayerUnknown’s Battlegrounds, Fortnite: Battle Royale has 100 people jump onto an island and fight to outlast everyone else. Unlike PUBG, Fortnite has a lot of polish and runs well on consoles. That has led to the game taking over the world and attracting celebrity players like hiphop artist Drake. Fortnite is so popular that it could threaten some of the Call of Duty’s revenues this year if console shooter fans stick with the latter instead of jumping onto the new release of the former.

Fortnite on iOS is a huge win for Epic on a number of fronts. Even though it is invite-only, it shot to the top of the iPhone download charts┬áhours after it launched. Reaching the top half of the iOS grossing chart also means a significant boost to revenues. But even more fundamental to Epic’s business model (at least what was its core business until now) is that the company is showing other developers how easy it is to bring a game out on PC, consoles, and mobile.

Epic makes the Unreal Engine game-development tool, and one of the studio’s primary sales pitches is that Unreal scales up and down to run on all kinds of hardware. But Fortnite also gives Epic an opportunity to work on some of the other features it has built out for Unreal over the last couple of years. Those include backbones for selling microtransactions and providing a game environment that runs well online.

Fortnite also enables Epic to test crossplatform multiplayer. While you can choose to play only against other people on mobile, Fortnite: Battle Royale has an option to let people play together on PC, console, and iPhone. That runs counter to competitive-shooter orthodoxy, which has always maintained that PC would have an unfair advantage with mouse-and-keyboard. But Fortnite is showing that might not matter if your game is popular enough. Additionally, Epic has baked in support for mouse-and-keyboard on mobile and even consoles.

So you can expect Fortnite to make Unreal Engine better through new product releases for other developers, but I’m sure Epic doesn’t mind that it is also generating so much money in the meantime.