This iPhone Duo app uses my handwriting to make it feel like it was made just for me

Apple's iPhone Duo is unlike any other iPhone that's come before it. When you're on the go, the device folds in half to create a small, back-pocket phone. When you're relaxing on the couch, it unfolds into a 7.6-inch iPad mini-like tablet. Because it's so different, the Duo brings new kinds of apps with it too.

The most interesting new iPhone Duo app is Fineliner. It's a note-taking app that mimics a pocket notebook. And since the iPhone Duo supports handwriting with the Apple Pencil (USB-C), the phone can be used for jotting down notes on the go.

I've used Fineliner on an iPhone Duo, and it works well. It's straightforward to get started with. But its special sauce is its interface. You begin using the app by drawing yourself and then tracing some icons.

The little reveal officially happens when you draw a trashcan icon. After you do that, the default one on screen is replaced by your version. You're not just getting acquainted with drawing on the Duo. You're also creating the app's interface in your style.

After a few icons, you can skip the process if you'd like. I did that initially because I wanted to see other parts of the app. But it didn't take long before I went into the settings menu and finished drawing the rest of the icons. The whole process is fast.

To go even further, Fineliner will let you write out the entire alphabet so all the words and pictures in the app look like they're from you—like you created this app. It makes the interface ultra-personal. There just isn't anything else like it.

If the personalization wasn't enough, you can even export your icons and writing to send to someone else. So, other people can import your typography and customizations. Or you can just back up your style.

If any of this is tempting, the app is free to download and use. You get unlimited notebooks to use. More paper styles and colors are available for a fee in the app's "stationery store."

Other notable iPhone Duo apps

The app Deck-Man mimics a cassette player. Toastie is a game that uses the folding mechanics to act like a panini press. Put the ingredients on the sandwich inside the phone, then fold it closed to cook it.

There's the app Tiny Computers that makes the iPhone Duo look like retro laptops. You can even use the on-screen trackpad to move the cursor and play games like Solitaire. The computer replicas are so realistic that in some photos it can look like a real, full-sized computer instead of a phone app.

Several of these apps are paid and require a one-time upfront fee. But if you're looking for free apps to try on the Duo, then there are several good, unique ones as well. Netflix, MLB, Nightsky, NBA, Wikipedia, and other developers have all revamped their apps to take advantage of the new form factor.