The new operating system for Apple's Mac computers is now available free of charge, Apple has announced.
"The days of spending hundreds of dollars to get more out of your computer are over, " Craig Federighi, Apple Inc. Senior Vice President of Software Engineering told an audience at an Apple product event in San Francisco.
Apple has kicked off a product event at which the company is expected to introduce slimmer, faster iPads in time for the holidays.
The new tablets will face stiff competition, with Microsoft Corp, Nokia and Amazon.com Inc all plugging rival devices in coming months.
Apple, which jumpstarted the tablet computing market in 2010 with the first iPad, has already come under increasing pressure from cheaper devices from Amazon's Kindle Fire to Samsung Electronics Co Ltd's Note.
Technology giant Nokia has launched a raft of new products including its first Windows tablet device and two new large-screen smartphones, or "phablets".
The new Lumia 2520 tablet, designed to "work anywhere", was unveiled at a news conference in Abu Dhabi.
Two new 6in (15cm) screen smartphones, or phablets, were unveiled - the Lumia 1520 and Lumia 1320 - offering easier access to apps and other new features.
"At Nokia we have found that tablet usage peaks between six and eight in the morning and between six and nine in the evening. During the rest of the day tablet usage drops quite dramatically," Nokia chief executive Stephen Elop said.
"We are looking to shift this trend - your tablet should be as mobile and as connected as you are."