Behind the Scene: Riley Testut's Unconventional iOS Odyssey – From Delta to AltStore

 

As many of you know, the birth of GAMEBABY—our wildly stylish gaming phone case—owes a huge creative debt to a pivotal piece of software: Delta. For the uninitiated, Delta is a legendary iOS emulator that effortlessly resurrects classic games from platforms like NES, Game Boy Color, and Game Boy Advance right on your iPhone or iPad.

 

But here’s where it gets fascinating: the mastermind behind Delta is Riley Testut—the same boundary-pushing developer who gifted iOS users AltStore, a revolutionary sideloading haven. In Apple’s ecosystem, Riley’s projects aren’t just ambitious; they’re rebellious. Naturally, we were itching to learn more about this maverick creator.

 

So when we finally connected with Riley recently, we seized the chance to dig into his mind—and brought back some insights you won’t want to miss.

 

「About Delta」

1.Many people know you as the developer behind Delta and AltStore, but how do you define the role behind the name “Riley Testut”? Please give us a brief introduction to yourself.

 

I was born in Texas, but spent most of my childhood in New Zealand so I’m a dual NZ/American citizen.

 

I’ve loved video games ever since I first played Super Mario Bros. with my Dad on his NES as a toddler. My first dream job was to become a video game programmer, but then this morphed into becoming an app developer once I got my first iPhone in middle school and fell in love with it. 

 

So it’s definitely a full circle moment making an app dedicated to playing classic video games :)

 

2.Back when the App Store had strict limitations on emulator apps, what made you decide to launch Delta on iOS?

 

I had previously released a Game Boy Advance emulator (GBA4iOS) as an open-source side-project in high school, and it became much more popular than I expected. 

 

 

So I decided to build a new app from scratch that could emulate more systems than just GBA — but primarily because I just wanted another side-project to help me learn Swift (which had just been announced by Apple). I didn’t plan on making Delta a “real” app until later.

 

 

3.Has Delta required any special technical implementations to support cross-platform emulation (such as NES, SNES, GBA, etc.)? And did you encounter any particular challenges dealing with iOS’s sandboxing restrictions?

 

I’ve structured the Delta codebase in a way that abstracts the differences between each system into a single “DeltaCore” framework, which makes it very easy to add additional systems later. 

 

 

Thankfully sandboxing didn’t pose an issue with Delta, as emulators are fairly self-contained.

 

4.How does Delta balance between recreating the retro handheld gaming experience and offering a modern software interface? What’s your take on dedicated accessories like GAMEBABY in terms of usability and creative value?

 

A lot of effort and experimentation! 

 

Our designer Caroline Moore works carefully to design controller skins for each system that can accommodate a wide variety of play styles, while also embracing the look and feel of the respective system. 

 

 

This allows Delta to be used as conveniently as possible with just touch controls — but there’s no doubt physical controls are better for games, which is why GAMEBABY and other accessories are great ideas.

 

 

 

5.Since playing retro games inevitably raises copyright concerns, how do you view the boundary of “legal use” for emulator apps? Do you think developers have a responsibility to better inform users about this?

 

Emulators themselves are perfectly legal. The issue is more related to how to acquire games, which is why we direct our users to products such as the GB Operator to make their own legal, digital backups.

 

6.Are there any plans for Delta to expand to more platforms, such as macOS, tvOS, or even ecosystems beyond Apple’s?

 

We’d love to make official macOS and tvOS ports (as well as visionOS!), but we are prioritizing other features in the meantime so we don’t have any immediate plans. 

 

We also don’t plan to ever expand beyond Apple’s ecosystem, primarily because I’m just an iOS developer.

 

7.Why did you choose to open-source Delta and offer all core features for free? Beyond the current supporter perks, are you considering more paid unlockable features in the future?

 

Easy answer: the licensing for the various emulator cores in Delta requires that Delta itself is open-source. 

 

We also don’t plan to add more Patreon perks beyond custom app icons and access to Experimental Features at the moment, but there are several new Experimental Features we plan to release soon!

 

「About AltStore」

 

8.Noticed that you also created AltStore, the well-known third-party sideloading platform for iOS. Could you share the origin story behind this project?

 

A few months after I first starting developing Delta in 2016, I asked Apple directly at WWDC if they would approve Delta for the App Store if I submitted it. 

 

To my surprise they said yes, so I spent the next year building a version of Delta I could submit to the App Store. Unfortunately the next year they changed their minds and said Delta would not be approved, giving me no choice but to build my own way to distribute Delta.

 

I spent the next couple years building such a system, then finally released AltStore (and Delta) in 2019.

 

 

9.Apple has been gradually easing restrictions on third-party apps and developers in recent years, which has positively impacted both Delta and AltStore. How do you view these shifts in Apple’s app ecosystem policies?

 

Great! It shows competition is already working thanks to the EU’s Digital Markets Act, and gives me hope we will continue to see more changes as AltStore PAL and other third-party app stores grow in Europe.

 

 

10.Many developers have criticized the App Store’s review process as lacking transparency. Have you ever encountered any review-related disputes, and how were they resolved?

 

We initially tried to include a link to our Patreon in the App Store version of Delta, but this was rejected because of their anti-steering rules. 

 

After some back-and-forth, we’re now allowed to show a link to our Patreon and unlock Patron-exclusive benefits — but only in the US App Store version of Delta thanks to Epic Games’ lawsuit against them https://www.theverge.com/2024/1/16/24040881/apple-outside-payments-app-store-policies-iphone-ipad

 

11.As a developer, how do you see the current relationship between Apple and developers? What aspects of the App Store—such as revenue sharing, review rules, or promotion mechanisms—do you find unreasonable or in need of improvement?

 

It’s pretty awful. I’ve never seen such disdain for Apple from the indie dev community, which traditionally has been some of the most ardent Apple supporters. At this point the relationship between Apple and developers needs a complete reset, which includes yes better revenue sharing but also better everything.

 

「About GAMEBABY」

 

1.When did you first learn about the GAMEBABY?

 

Last September when I saw it on MacStories: https://www.macstories.net/linked/bitmo-lab-opens-pre-orders-for-a-delta-emulator-friendly-iphone-case/

2.What is your opinion on hardware products like GAMEBABY?

 

Love them! We need more quirky, fun ideas like this in the world (especially right now…), and I think GAMEBABY fully embraces the notion that an iPhone can be whatever you want it to be.