WatchOS

watchOS is the mobile operating system of the Apple Watch, developed by Apple Inc. It is based on the iOS operating system and has many similar features. It was released on April 24, 2015, along with the Apple Watch, the only device that runs watchOS.
The second version, watchOS 2, included support for native apps that could be made for the Apple Watch and other improvements, and was released on September 21, 2015. The third version, watchOS 3, was released on September 13, 2016, It had better performance and including new watch faces and stock apps. The fourth version, watchOS 4, was released on September 19, 2017. The fifth version, watchOS 5, was released on September 17, 2018, adding more support for apps that could be made for the Apple Watch and new workouts, along with the “Walkie-Talkie” feature.