CloudKit

CloudKit is an integrated macOS, iOS, iPadOS, watchOS, and tvOS API that functions as a backend as a service (BaaS).

[1] CloudKit is the framework that powers iCloud on those operating systems and on the web.

The framework provides authentication, a private database, a public database and structured asset storage services allowing developers to focus on client-side development.

[3] CloudKit also offers several APIs to access the iCloud Storage, where a user can store data and files so that they can be easily accessible from other devices.

[4] Developers claim that this framework "replaces back-end web services like old-school databases, file storage and user authentication systems.