IOS 9

iOS 9 is the ninth version of iOS, which was released on 16 September 2015, and was first announced at WWDC 2015 on 8 June 2015.

3D Touch
Support for 3D Touch has been added for iPhone 6s models. It allows for pressure-sensitive gestures to be performed. It would be replaced by Haptic Touch in iOS 13.

Intelligence
Siri Suggestions has been added, which will provide quick actions and shortcuts based on time, location, and device activity. Suggestions can be viewed on the re-added search page on the Home Screen, as well as in supported applications.

Low Power Mode
Low Power Mode has been added to help users conserve battery life. It disables background app refresh, push email, and certain UI animations.

Night Shift
iOS 9.3 adds Night Shift, which shifts the colors of the device's display to be warmer. It is only available for 64-bit devices.

Multitasking

 * The App Switcher has been redesigned.
 * Slide Over, Split Screen, and Picture-In-Picture was added to certain iPad models.
 * Opening an app from a notification will provide a back button in the status bar.

Notification Center

 * Notifications can now be grouped by which app it came from.
 * The battery widget has been added to the Today view.

Keyboard

 * Shake to Undo can now be disabled.
 * When the shift button is inactive, lowercase letters are displayed on the keyboard
 * On iPad, a two-finger drag on the keyboard can be used to move the cursor. This feature is also available on iPhone 6s models by using 3D Touch.

Apple News
The News app has been added, which replaces Newsstand. It organizes news from different sources and recommends articles based on the user's interests.

Photos and Camera

 * Support for Live Photos has been added.
 * The photo viewer now has a scrubber bar for quickly scrolling through items.
 * Photos can now be hidden.

Safari

 * Safari now supports third-party content blockers.
 * Reader Mode can now be customized.

Wallet

 * Passbooks has been renamed to Wallet.
 * Support for Discover credit/debit cards, loyalty cards, and gift cards has been added.
 * Cards can now be accessed from the Lock Screen.

Health

 * Sleep, exercise, and weight data from the Apple Watch will now be synced with the Health app in iOS 9.3.
 * Support for reproductive health, UV exposure, water intake and sedentary state data types has been added.
 * The app can now be viewed in Landscape Mode.

Miscellaneous

 * The San Francisco font is now used as the default typeface.
 * The Settings app now includes a search box.
 * Wi-Fi Assist has been added, which automatically switches the phone to cellular data when the Wi-Fi connection is spotty.
 * The Metal API is now used for core UI elements and graphics.
 * Updates are significantly smaller in size.