You write a letter in the Foldwriter app by half-folding the iPhone Duo, with the paper above the hinge and the keys below it. When the letter is done, you close the phone, and the outer display swaps the sheet for an envelope that you address, stamp and send.
Foldwriter is on the App Store and sits alongside Halfpage, Post Club and Foldtype, the other typewriter apps for the iPhone Duo. It differs in how a page ends, because you stamp the letter and send it to someone through the share sheet.
The Foldwriter app has three typewriters
You pick between three machines, and each has its own recorded key sounds, carriage movement, bell and haptics.
- Sunday is a hooded 1950s portable with pillow keys
- The Editor is a 1920s desk machine with glass keys on levers
- Rosso is a red 1969 pop portable with square keys
You half-fold the iPhone Duo and type on the lower half, with the paper above the hinge. Backspace moves the carriage back without erasing anything, so you type over your mistakes. When you open the iPhone Duo flat, the keyboard splits.
Close the phone to address the letter
Tapping Pull page, or closing the phone, swaps the sheet for an envelope on the outer display. You type a name, choose one of five original stamps, and the envelope gets a dated postmark.
After you tap Post, the send screen offers Send the letter, Save image and More formats, with Keep typing and New page below them. The send screen also appears on the outer display, so you can post the letter without opening the iPhone Duo again.
Foldwriter sends the letter through the share sheet as an image, a vector PDF or a short video. The video re-types the letter key by key with the sound of your machine, and the person who receives it does not need the app.
Foldwriter costs $1.99 once
Foldwriter has no in-app purchases, subscription or ads, and it comes from Richard van Yperen, an independent developer in the Netherlands. The 4.1 MB download supports English and Dutch and installs on iOS 17 or later, while the fold layouts on the iPhone Duo need iOS 27.1.
The app also works on every other iPhone and with a hardware keyboard. It collects no data, needs no account and has no network access.
