Apple WatchKit ➝

Apple released WatchKit:

WatchKit apps have two parts: A WatchKit extension that runs on iPhone and a set of user interface resources that are installed on Apple Watch. When your app is launched on Apple Watch, the WatchKit extension on iPhone runs in the background to update the user interface and respond to user interactions. WatchKit provides three opportunities to extend your iPhone app to Apple Watch: WatchKit apps, Glances, and actionable notifications.

See also, Apple Watch Human Interface Guidelines.

A whole new toy.