RxSwift
Reactive Programming in Swift
...Like other Rx implementation, RxSwift's intention is to enable easy composition of asynchronous operations and streams of data in the form of Observable objects and a suite of methods to transform and compose these pieces of asynchronous work. KVO observation, async operations, UI Events and other streams of data are all unified under abstraction of sequence. This is the reason why Rx is so simple, elegant and powerful.