Apple is to make developers able to make apps for its wearable Apple Watch for the first time ever.
Apple says app developers will be able to make apps specifically for the watch and interact directly with the watch's sensors and controls, such as the dial.
Third-party apps for the Apple Watch have been limited to being extensions of apps that run on the iPhone. With native app support, third-party fitness apps will be able to work without a phone nearby.
Currently, only Apple's own Activity and Workout apps do that.
Apps will also be able to play audio using the watch's speaker and tap its microphone.
The next version of Watch OS will also have new watch faces, including those featuring your personal photos and albums. Raise your wrist, and a different photo from the album shows up.
App developers will also be able to design information modules known as "complications" to appear on the watch faces. An airline, for instance, might design one with upcoming flight times.
A new feature called Time Travel will let users scroll the dial to go back and forward in time, whether that's for upcoming meetings or weather forecasts. Sadly, Apple says Apple Watch can't offer future stock prices yet.
The new features were unveiled Monday at Apple's conference for developers in San Francisco.
"We believe in technology designed for the wrist", said Mr Cook, discussing the new version of Apple Watch software, called watchOS.
Apple's Kevin Lynch took to the stage to show off the new features of watchOS, including new watch faces, which can be made up of images for the first time.
Timelapse photos shown as live, based on the time of day, can also be used.
Mr Lynch also showed off "Time Travel", a feature that will enable users to scroll forward and back to see the different parts of their schedule. "Flux Capacitor sold separately," said the message on-screen.
The drawings in Digital Touch can now also be done in a range of colours.
The Apple Watch will also support short video playback on the watch face, including from apps such as Vine.
Siri can now also be used to control aspects of your smart home, asking it to change lighting for example, as well as ask the digital assistant to show the Glance notifications that run on Apple Watch.
An Apple Watch was also shown controlling the temperature inside a connected car, as well as using voice to reply to emails.
The new watchOS will launch in the autumn, it was confirmed.
Additional reporting by Press AssociationReuse content