What is a cross-platform app?
A cross-platform app is built once and runs on more than one platform, usually iPhone and Android. Frameworks such as React Native and Flutter let developers share most of the code, and each has its own way of drawing the screens.
More about Cross-platform app
Sharing code saves work when an app must be on both platforms. The cost is a layer between the app and the system: new iOS features and designs reach it later, and parts that use the phone's hardware often need native code anyway.
Cross-platform app with Borel
Borel is made for iPhone and writes each app natively in Swift with SwiftUI, so your app uses Apple's own controls and frameworks directly. You describe it once, in plain words, and Borel takes care of the code.
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Make your iPhone app in Borel
Describe it in your own words. Borel writes it in Swift, builds it on its own Mac and puts it on your iPhone.