watchOS apps

App Frameworks

Official docs outline

Essentials
Covers Creating an intuitive and effective UI in watchOS 10, Updating your app and widgets for watchOS 10, Building a watchOS app, watchOS updates.
App experience
Covers Setting up a watchOS project, Creating independent watchOS apps, Keeping your watchOS content up to date, Updating watchOS apps with timelines.
Accessibility
Covers Create accessible experiences for watchOS.
User interface
Covers Building a productivity app for Apple Watch, Supporting multiple watch sizes, Designing your app for the Always On state, Setting the app’s accent color.
Complications
Covers Creating accessory widgets and watch complications, Migrating ClockKit complications to WidgetKit, Creating a widget extension, Keeping a widget up to date.
Notifications
Covers Notifications.
Siri
Covers Making actions and content discoverable by Apple Intelligence, Creating an Intents App Extension.
Health and fitness
Covers Setting up HealthKit, Authorizing access to health data, Saving data to HealthKit, Reading data from HealthKit.
Runtime management
Covers Background execution, Life cycles, Using extended runtime sessions, Interacting with Bluetooth peripherals during background app refresh.
Network requests
Covers Making default and ephemeral requests, Making background requests.
Unit tests
Covers Setting up tests for your watchOS app.

Each section links to the official page. Titles and summaries by Extra Credit; the docs belong to their authors.