DOSSIER 002 · FIELD NOTES
10 coolest examples of what to build for the Duo
Ten clever apps and experiments builders have shared for Apple's foldable iPhone Duo, and what they get right about the hinge.
Apple announced the iPhone Duo, its first foldable iPhone, on 9 September. It goes on sale on Friday 23 October, including here in Australia. Closed, it's a 5.4 inch phone. Open, it's a 7.6 inch screen, and both screens share the same aspect ratio.
Developers have spent the weeks since the announcement working out what to do with it, and a lot of what they've shared on X is genuinely good. The builds I like most don't treat the fold as a way to get a bigger screen. They make opening and closing the phone part of how the app works.
Here are the 10 that stood out to me. None of them are mine. Each one links to the builder's own post, so go and give them the credit.
1. Duo-Man by @viditb
Duo-Man turns the Duo into a Walkman. You open the phone to pick a cassette and "insert" it, then close it to start listening. He recorded the button clicks and static from a real Walkman, which is the kind of detail that makes it feel like an object rather than an app. He built it at a Bitrig hackathon, and the post has passed 10,000 likes.
2. PianoDuo by @Brian_Corrieri
PianoDuo is Brian's second Duo game. The top screen becomes a window into your room using the live camera, and piano tiles flow toward you through it while you play melodies from well-known classical pieces. It's due on 23 October, the same day the phone ships.
3. Guitar Pocketbook by @wwwalkerrun
This one uses the fold as a mixing control. Changing how far the phone is folded changes the reverb and tone, and the hinge glows in time with the audio frequency. It's built with NativeScript, with the audio graph written in TypeScript.
4. DS Store by nicolapps
The Nintendo DS had two screens stacked on a hinge, so this was always going to happen. DS Store is a SwiftUI emulator built on melonDS that puts one DS screen on each panel of the Duo. It was made by nicolapps and spotted by @DuoRegistry.
5. Trading-card binder by @erekle_meskhi
With the phone closed, the outer screen holds a sealed pack. You swipe across the top to tear it open, then unfold the phone and the cards rise out of the fold. Inside, the binder rings sit on the hinge and each page turns across it. It's a good example of the closed and open states doing different jobs.
6. CREASE by @playcrease
CREASE is a table game that changes with the phone. Open, it's a full table for two players, one on each side. Closed, it's a pocket table where you play the CPU. You can fold it mid-match and the game keeps going. It's free and runs in the browser, so you can try it before you even have a Duo.
7. Pop-up photo cards by @lj_ships
This is a pop-up card app. You pick a photo, open the phone, and the people in the photo stand up out of the fold, like a paper pop-up book. On a regular iPhone a slider does the job. On the Duo the hinge does it. It's built with @JolinJiao and aimed at launch day.
8. Angled
Angled turns the hinge into a protractor. Each day there's a hidden target angle, and you fold the phone by feel to hit it and keep your streak going. If you don't have a Duo, a tilt mode works on any iPhone. It's still being built, with an App Store release planned. @DuoRadar shared it.
9. Papelle by @itspaolopv
Papelle is a greeting card app that @itspaolopv made with his wife, with handcrafted cards, some of them illustrated by him. Open the Duo and the cards, photos and even videos come alive with the hinge. You can pause, close and reveal them. It's up for pre-order now.
10. Detail
Detail, from Detail Technologies, turns the Duo into a three-camera rig for creators. You can take selfies with the rear camera while the outer screen shows the preview, read from a teleprompter that sits beside the lens, and use Book Mode to record the front and rear views at the same time. It's already out. @DuoRadar shared it.
What I take from this
Most of these are small apps, and several are one person's side project. That's the point. A new form factor gives you one idea nobody else has had time to build yet, and the hinge is it. Stretching an existing app across a bigger screen won't stand out. An app that only makes sense when you fold the phone will.
If you're building for the Duo, start with the fold and work backwards.