watchOS

watchOS is the dedicated operating system for Apple Watch, delivering powerful, on-wrist access to health, fitness, and communication tools.

watchOS is the core software platform for Apple Watch, engineered for speed and immediate utility: it's not a scaled-down iOS, but a purpose-built OS. The platform excels in health tracking, leveraging sensors for metrics like heart rate, blood oxygen, and ECG readings. Recent versions, including watchOS 11, introduced the Vitals app for overnight health data analysis and the Training Load feature to optimize workout intensity . Users interact via the Digital Crown, Taptic Engine, and a redesigned Smart Stack for quick access to contextual widgets . Developers utilize the WatchKit API and SwiftUI to build native apps, complications, and rich notifications, ensuring a seamless, glanceable experience on the wrist .

https://developer.apple.com/watchos/