Apple yesterday released watchOS 2 to the public, making the first major update to the watchOS software available to all Apple Watch owners. The update requires iOS 9 and can be downloaded over-the-air through the Apple Watch app on the iPhone by going to General --> Software Update.
watchOS 2 was originally scheduled to launch on Wednesday, September 16 alongside iOS 9, but Apple delayed the launch in order to address a major bug that was found shortly before the software was set to debut.
As the first significant update to watchOS, watchOS 2 introduces a lot of new features to the Apple Watch, mainly through new developer tools. watchOS 2 brings native apps that run on the watch itself instead of the iPhone, and it lets developers access several sensors and hardware features including the Taptic Engine, heart rate monitor, microphone, and accelerometer.
Along with these features for developers, which will lead to more complex and full-featured third-party apps that run much more smoothly, watchOS 2 also includes new watch faces (photo album and time-lapse), third-party Complications, a tweak that makes the screen stay on for up to 70 seconds when activated, and Activation Lock.
There's also a new Time Travel feature for viewing past and upcoming events in a watch face Complication, and a Nightstand mode that's activated when the watch is charging, displaying the time.