Riley Testut has spent the better part of the last decade trying to sneak in through the side door of the iPhone. Since he was a teenager, the Dallas-Fort Worth native has been fascinated with app development — in particular, with emulation technology that allows modern computing devices to run the video game software of decades-old game consoles.

Yet Testut, a longtime Apple fan, was disheartened when he came to realize that classic video games from developers like Nintendo would never make their way onto the official iOS App Store. Nintendo has no interest in porting its games to iOS — it has since opted to make mobile-specific versions instead — and Apple has always had strict policies against apps that can be used for piracy. So Testut decided to try to build the emulation technology that would let you do it yourself.

AltStore is a way to distribute iPhone apps that are not allowed on the official App Store

“As a kid, I played all these games, and so I just came across some code that I thought I could turn into an app to play Game Boy games, and that just started a whole thing,” Testut says. “I just found myself in this whole emulation scene. I probably don’t know if I would have picked it really if I had thought through everything. Because it’s a lot to work on these apps, knowing that they’re not going to be in the App Store ever.”

His initial emulation work, spanning the last two years of high school, resulted in a Game Boy emulator known as GBA4iOS. It made headlines in 2014 when both Apple and Nintendo moved to shut his project down. (GBA4iOS lived on for some time, thanks to a clever loophole, but it is no longer available.)

Now, Testut, a 22-year-old freelance software developer living in Los Angeles, may have figured out a way for his software to live on Apple’s iOS platform for good. He calls it AltStore, and it’s an alternative mobile app distribution platform that lets anyone download software that’s not available on the official App Store.

The store’s very first app: Delta, a GBA4iOS successor Testut has been building since well before he entered the University of Southern California a half-decade ago. The really interesting part is that none of it requires you to jailbreak your iPhone, so it’s available to anyone who’s willing to download it, for free.

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Delta is a powerful app with the kind of polish you’d expect from a major software maker. It lets anyone run corresponding game files for NES, SNES, Game Boy, Game Boy Advance, and even Nintendo 64 consoles. Testut is also working on Nintendo DS emulation and other related projects for future updates. It’s the kind of app Apple would never allow, but it’s also the kind of software iPhone users have been dreaming about for years.

“It’s more fun working on it for iOS because, yeah, on Android, I could just release a tiny [emulator]. But on iOS, I know that people want this. I know people want to relive those games. I also know that so many people have iPhones. I have an iPhone,” he says. “So I want to bring what I know people want to everyone. That’s really the motivation here.”

For Testut, AltStore arose from him just “wanting to get Delta out” and in the hands of people who’d want to try it. “It just made sense. If I’m building this whole process for Delta, just to build it out for anyone to use,” he says. “I’m also hoping that because I was so motivated to do this, and I build this whole process, other people can now start making more apps to bring to it. I’m doing it because I want to also improve the quality of apps that you won’t find in the App Store, but that could still exist on the platform.”

AltStore works, thanks to a clever combination of tricks that exploit how the iPhone is designed to be used by independent developers. It involves downloading a companion application called AltServer, which then takes your Apple ID and installs AltStore onto your iPhone, signing it as an app you’ve created yourself. But in reality, it’s Testut’s software. The same trick underpins software like Cydia Impactor, a popular tool for sideloading apps on iOS that arose in the years after jailbreaking fell out of fashion.

“AltStore basically lets you install apps outside the App Store by tricking the phone into thinking you developed the app yourself, like you programmed it and you installed it and you’re testing out your device,” he says. “A few years ago, Apple added the ability for Xcode, Apple’s developer tool, to allow anyone with an Apple ID to install their own apps on their phones, so that Apple could encourage people to learn to program iPhone apps and test them out.” Testut says AltServer is using the same process behind the scenes to get AltStore onto your phone.

There are some restrictions involved, like having to plug your phone in initially to install AltServer and having to refresh AltStore every seven days to sidestep an Apple restriction on self-installed apps. But Testut conceived a way to have your phone complete that refresh process over the internet using iTunes Wi-Fi sync. He launched AltStore last weekend after testing it extensively for months earlier this year, and the response he says has been astounding. He says he also hasn’t “heard anything from Apple or Nintendo, so taking that as a good sign for now.”

Those privy to the niche mobile emulation and iOS jailbreaking scene likely know Testut’s name. As the creator of GBA4iOS, Testut became a popular figure in emulation before he’d ever taken a college-level programming course, and it grew even more when he was able to sneak the software onto any iPhone, thanks to a clever workaround involving what’s known as the Apple Developer Enterprise Program.

The enterprise program is a software platform Apple designed to let large corporations distribute private apps, be it for testing or for internal company operations. But Testut suspected Apple wasn’t keeping a close eye on who applied for the $300-a-year license to access the platform or what they were doing with it. So he found a company that sold the certificates (Apple parlance for the license to distribute private iOS software) and used that certificate to start distributing GBA4iOS to anyone who chose to download it from his website.

Of course, Apple caught on quick and revoked Testut’s certificate. Nintendo also targeted Testut’s GitHub account with a takedown notice for hosting the emulation code. While the legality of ripped game files, known as ROMs, is pretty clear-cut, the legality of emulator software is less so; it’s never been decided in court. But Testut wasn’t looking for a legal fight, and he yanked his code voluntarily.

He then embarked on a years-long project to turn GBA4iOS into something more powerful that he later called Delta. He began working on Delta in between freelance software gigs and a slate of classes at USC. Roughly a year ago, he announced that he would be shifting his attention to it full time after graduating.

Testut made headlines in 2014 when both Apple and Nintendo tried to shut down his emulator

In the years since GBA4iOS, the enterprise program has become the platform of choice for far more questionable and outright illegal software, from entire illicit app stores peddling cracked versions of popular subscription software like Netflix and Spotify Premium to knock-off video games, pornography apps, and torrent clients. Many of them are based in China and seem to have an endless supply of enterprise certificates of unknown origin; Apple may revoke one, but the stores, with names like TutuApp and AppValley, keep popping back up.

The enterprise program’s dark underbelly earned itself mainstream recognition earlier this year after it was discovered both Facebook and Google were using the same distribution trick Testut relied on for GBA4iOS to install apps that monitored teenagers’ smartphone behavior in exchange for monthly gift cards. Apple revoked both companies’ certificates over the apps, which were in violation of the enterprise program’s terms of service and would have never been allowed on the App Store in the first place.

But the renewed attention to the enterprise program and Apple’s lax enforcement marked a turning point for using it as a way to sidestep iOS restrictions, as Testut says Apple has since clamped down on access. Following his showdown with two of the biggest names in technology and the game industry, Testut started looking for safer ways to try to distribute his own software.

That’s what makes AltStore unique. It doesn’t require you to root your Apple device, which voids your warranty and potentially risks rendering your device inoperable, as most jailbreak techniques require. You also don’t have to hand access to your device to a company with unknown motives and suspect privacy policies and security measures, as is the case with many of the illicit app stores abusing the enterprise program.

AltStore may get shut down at any moment, but it’s not clear how Apple might do so

AltStore is a container for apps that you can’t find on the App Store, and it’s as easily accessible on the iPhone as any app on the web is on your Mac. In many ways, it represents a bold view of what iOS might look like if it incorporated more of Google’s philosophy around user freedom that we see with Android, where users have been sideloading apps, including emulators, for years.

But whatever changes Apple makes to iOS down the line, either to appease increasingly frustrated app makers or avoid potential antitrust regulation, the reality now is that Testut could get shut down at any moment. That would spoil his plans to turn AltStore into a budding experimental platform for other developers to use. The big question is how would Apple do it, and what might be the ripple effects.

Testut says he’s not sure it would be easy for Apple to remove the ability for independent developers to sideload apps without also doing so for DIY developers, schools, and other organizations that build test apps and software for personal and internal use.

“It would be interesting because everything I’m doing, Apple is doing themselves,” Tesut says. “One heavy-handed approach is [Apple] could completely shut down the whole service. But that would affect everyone doing this, including schools, anyone just using their free Apple ID on the side.”

Besides that, Testut imagines Apple could disable the ability to sync over Wi-Fi, but that would just mean plugging in your phone once a week to continue using AltStore and the apps it distributes. “I don’t know how fast they’d react and what they would do. But even in the worst case, I think there’s still a path forward for AltStore. As long as iTunes can sync apps,” he says, “AltStore can work.”