Combine is Apple's unified declarative framework for processing values over time. It aims to simplify asynchronous code like networking, key value observing, notifications and callbacks. It is available on iOS 13 and up.
Why is this technology in trial?
Combine introduces first-class reactive programming to the Apple platforms without the need for external frameworks like RxSwift and ReactiveSwift.
Combine will undoubtedly gain more traction with SwiftUI getting adopted. Both sharing the reactive programming paradigm, they tie together nicely.