Apple Watch, announced in September with first deliveries scheduled for early 2015, serves as a digital or analogue watch, a health and fitness monitor, and a contactless payment device.
Its user interface include the Digital Crown (in place of a conventional watch's winder/adjustment knob, which is known in the trade - if not in everyday language - as the crown), Force Touch (a force-sensitive touch screen) and the Taptic Engine (the name is a portmanteau of 'tap' and 'haptic,' referring to the way it allows the watch to alert you with a tap on the wrist).
The arrival of the iOS 8.2 SDK with support for WatchKit means developers can now start work on apps for Apple's forthcoming wearable.
"With the iOS 8.2 beta SDK, developers can now start using WatchKit to create breakthrough new apps, Glances and actionable notifications designed for the innovative Apple Watch interface and work with new technologies such as Force Touch, Digital Crown and Taptic Engine."
One of the ways Apple expects the Apple Watch to be useful is by providing snippets of important or at least significant information, which the company calls Glances. Examples include sport scores, news headlines, and travel information.
Companies that have been able to preview WatchKit include ESPN and American Airlines.
ESPN executive vice president of digital and print media John Kosner said "Fans crave real-time and personal information, and the ESPN app for Apple Watch gives us the ability to deliver live scores and information for their favourite teams."
"Glances provide fans with a snapshot of live games, and if there is no game taking place, they'll get valuable game-time information or the final box score," he added. "With actionable notifications, the experience becomes even more personal, as fans receive alerts on score changes, news and more."
American Airlines vice president of digital John Gustafson said "The American Airlines app on Apple Watch reminds you when it's time to head to the airport via pre-trip notifications, and provides updates for gate changes, connecting gate info upon arrival, and will notify you when boarding begins if you're not at the gate yet.
"Travellers can also ask 'Where am I?' in-flight and get real-time location information at 30,000 feet."
But it seems the beta SDK only provides developers with access to a subset of Apple Watch features. According to Apple, developers will be able to create fully native Apple Watch apps beginning "later next year."
The iOS 8.2 beta SDK is available for download by all iOS Developer Program members.