New Features
Every iOS device has access to new features like News — a Flipboard-like news aggregator — and a vastly improved Notes app, with support for checklists, photos, maps, URLs, and sketches. Maps once again has public transit directions, and Passbook — rechristened as Wallet — supports various store and rewards cards.
iPad-centric Features
Although it launched on all iOS devices this fall, iOS 9's prime destination was arguably the iPad. Only iPad users have access to Slide Over, Split View, and Picture in Picture — multitasking features bringing the tablet one step closer to being a bonafide computer.
Siri and Search
Apple is placing a large emphasis on search and Siri functions. Users can set contextual reminders with the Siri command "remind me about this," for example, or see things like suggested contacts, apps, places, and news items in search. The OS is also designed to be proactive, offering up actions and information based on past app habits.
System Improvements
A full list of improvements could be endless, but it's worth mentioning things like better battery life, smaller update sizes, and security measures like six-digit passcodes and two-factor authentication.
Tips:
William Gallagher
Roger Fingas
Mike Wuerthele
Neil Hughes
Mikey Campbell