Apple's iOS 7 will arrive on the iPhone 5, iPhone 4S, and iPhone 4 on September 18th. The all-new OS will also head to the iPad mini, the second-, third-, and fourth-generation iPads, as well as the fifth-generation iPod touch on the same day. In today's keynote, Tim Cook boasted that the operating system will soon be "the world's most popular operating system."

Announced back in June, iOS 7 is the first major visual overhaul of the OS since its initial introduction in 2007. It features all-new icons along with redesigned core apps, a new Notification Center, webOS-inspired multitasking, and a Control Center with settings toggles, music playback, and quick shortcuts to apps. There's also AirDrop for local file sharing over wireless, and even Apple's attempt at a Spotify and Rdio competitor in iTunes Radio.

There were a couple of small feature additions today, including a male voice for Siri for the US and select other territories. Apple also showed off a number of "remastered" ringtones, along with a brand new tones. To go with the new launch, Apple is making some of its big-name apps, including iPhoto, iMovie, Pages, Numbers, and Keynote, absolutely free.

The big news comes along with the new iPhone 5S: iOS 7 is now 64-bit compatible. All of the included apps run in 64-bit, and Apple says developers will have a "seamless" transition to port over to 64-bit apps.

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