WatchOS (stylized by Apple as watchOS) is the operating system of the Apple Watch, developed by Apple Inc. It is based on the iOS operating system and has many features similar to those of iOS. It was first released on April 24, 2015, alongside the Apple Watch. The Apple Watch is currently the only device that runs WatchOS. The API is called WatchKit.At WWDC 2015, WatchOS 2 was previewed publicly for the first time. It included major improvements such as support for native third-party apps,.