What is Xcode?
Xcode is Apple's integrated development environment (IDE): the app developers use to write, build, test and ship software for Apple's platforms. It includes the Swift compiler, the iOS Simulator, live previews and the tools that sign an app and upload it to App Store Connect. Xcode is free, but it only runs on macOS.
More about Xcode
Because Xcode needs a Mac, building an iPhone app has traditionally meant owning one. There is no Xcode for Windows or Linux, which is why people look for cloud Macs, or for services that do the Mac part for them.
Xcode with Borel
Borel runs Xcode on its own Mac, so you don't need one. When you describe or change your app, Xcode compiles it there, and the result streams to your browser in the iOS Simulator. When you publish, Xcode archives and signs the app on Borel's Mac and uploads it to App Store Connect.
Related terms
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.