Perhaps the biggest -- or at least the most instantly noticeable change -- is the look of the interface. The general layout to the home screen looks similar, but keyboards, the notification center, and a new control center all take on a clean, almost transparent look.
Messages, calendar, phone, Safari and game center all received similar refreshes, taking on the new iOS's airy appearance.
Software vice president Craig Federighi got a huge ovation for comprehensive multitasking, a feature iDevice users have clamored for since the iPhone's introduction.
"Smart" multitasking balances power between apps to maximize battery life efficiency, learning which apps get the heaviest use and when. Smarter updating also means apps will update in the background, and schedules updates when the phone is plugged in or connected to WiFi.
In addition to completely redesigned photo and camera apps, the new operating system also introduces AirDrop, which allows sharing photos, videos and contacts over WiFi and Bluetooth with anyone nearby.
The often-maligned Siri got a needed functionality boost, too. Voice commands can now control opening apps and can search more complex questions, tasks earlier versions of the app struggled to complete.
Finally, Apple has added a radio player to iTunes, aping the popular music programs Pandora and Spotify, which let users chose from predesigned playlists or design their own.
The new operating system, iOS 7, will debut this fall for iPhone and iPad.
Apple also previewed its next desktop operating system, OS X Mavericks.
The new system introduces several popular iOS apps making their desktop debut, including iBooks and Maps, with updates to Safari, a more powerful Finder, and better support for multiple displays.
Apple unveiled no new mobile devices at this year's WWDC, but it did introduce a new Mac Pro desktop and refreshed the MacBook Air notebook.
Justin Bieber crashes Drake Bell's album release party
Rosie O'Donnell unveils nearly 50-pound weight loss