#2 Windows 8

Microsoft's own Steve Ballmer once described Windows 8 as one of the three biggest initiatives the company has ever attempted, but we'd go even further. From small details like the tiled interface and the Charms sidebar to big-picture changes like the emphasis on touch and apps in the new Windows Store, Windows 8 completely revolutionizes the operating system.

The icon-based path Windows began walking in 1995 has taken a sharp turn toward mobility, interactivity, and independence. There's nothing out there that looks or behaves like Windows 8, and Microsoft is finally leveraging its weight to force manufacturers to up their game. Touch screens on all kinds of computers soon will be commonplace, and a new category of hybrid and convertible laptops is emerging. Neither of those things would be happening as fast as they are now if Windows 8 wasn't in the driver's seat.

It's not quite two months old, so it's hard to tell how successful Windows 8 has been so far. On the one hand, Microsoft says it sold 40 million Windows 8 licenses in the first month -- double Windows 7's adoption. And the Surface RT, running the stripped-down Windows RT, has been Microsoft's biggest buzz-maker in years. On the other, there's no question that Microsoft has missed its own internal sales projections.

The important question isn't about its success or failure, but what success actually means when you've already got around 90 percent of the worldwide computer market. Windows has been slowly slipping for years, but Windows 8 has given people a reason to give it a good look again.

For more on this story, see our full Windows 8 review.

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