Based on Microsoft's latest earnings report, its Surface RT is a flop. This, in turn, means that Windows RT has failed. But, there are many other would-be tablet operating system challengers to Google's Android and Apple's iOS. Seriously, though, do any of them have a real shot?

Just over a third of Americans now own tablets . As time goes on, more and more of them will be buying tablets over PCs. By 2017, market research firm NPD predicts that we'll be buying six tablets for every single notebook . Of these tablets, most experts agree it's only a matter of time before Android is on top of the tablet mountain.

That's not to say Microsoft has no hopes for the tablet form factor. I believe Microsoft has a real shot of being a viable third tablet choice if they elect to place its Windows 8.1 family operating system across all devices—PCs, tablets, and smartphones .

Does anyone else have a chance? Blackberry may have given up, but there are many others who want to dethrone Android and iOS. Here, are the leading contenders in the order I rank their chances.

1) Firefox: Firefox is actually ahead of Ubuntu on smartphones with its Linux-based Firefox operating system. For applications, Firefox will rely upon Web-based HTML5 apps. It's an unproven route, but as we put more and more of our apps on the Web and the cloud, it may be a workable one.

Unlike its other Linux-based rivals, Firefox OS smartphones, such as the Alcatel One Touch Fire and ZTE Open, are already shipping. Thanks to its Web browser, Firefox is better known outside of techie circles than Ubuntu and that's where the tablet audience lives. Mozilla, Firefox's parent organization, has long had its eye on tablets and, partnered with Foxconn, its first engineering sample tablets have started to appear .

2) Ubuntu: Ever since Canonical introduced the Ubuntu Unity interface I thought it had the potential to be a great tablet interface. While much of the news lately has been about Ubuntu's efforts to win supporters for Ubuntu on smartphones , Canonical has big plans for the Ubuntu tablet as well. Indeed, Ubuntu's founder, Mark Shuttleworth, has promised us that he'll be making a big announcement on July 22nd. I strongly suspect he'll be announcing major Ubuntu tablet news.

I've always been fond of Unity on devices, and I think Ubuntu has a real shot. For now, Firefox is ahead in actually shipping units. We'll see it's that still the case by year's end.

3) Sailfish: When Nokia turned its back on the MeeGo mobile Linux project and bought into Windows Phone, five Nokia staffers started their own company, Jolla, to keep pursuing an open-source operating system approach, Sailfish OS. Unlike Mozilla and Tizen, Sailfish relies on the old Linux stand-by Qt QML, instead of HTML5 for its apps.

Sailfish is on the verge of shipping its first smartphone in the Asian market. After that, Jolla would be more than happy to ship tablets .

4) Tizen: Tizen, like Firefox is an open-source, Linux-based mobile operating system that relies on HTML5 for apps. In theory, Tizen has Samsung's support . In practice, it's been an unwanted step-child without a clear roadmap . With its first device, a Samsung smartphone, pushed back from July to the fourth quarter, I doubt Tizen will ever live up to its promise.

That's a lot of potential players in the tablet space. All of them, except Microsoft, still aren't even really ready to compete yet. Perhaps in 2015, there will be a viable third-party tablet OS, but I really can't see it happening until then. In the meantime, Android and iOS will remain the top tablet dogs.

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