Hewlett-Packard Co's WebOS TouchPad after just seven weeks on shelves was a reminder of how tech giants have failed so far to take a bite out of Apple Inc's iPad. The TouchPad joins Dell Streak 5 in the tablet graveyard and weak sales for many offerings suggest others are bound to follow. Other tablets that have failed to click with consumers include Asustek Computer Eee Pad Transformer and the Xoom from Motorola Mobility, which Google Inc plans to buy.

"I do not expect RIM to be shutting down PlayBook sales any time soon or abandoning that platform, because RIM views it as its future," said Colin Gillis, an analyst at BGC Financial in New York.

Apple's rivals have not fared any better in designing software for tablets.

Apple's iOS tablet software accounted for 61.3 percent of the tablet market in the second quarter, more than double the 30.1 percent share held by Google's Android, its nearest competitor. Microsoft held a paltry 4.6 percent share and RIM 3.3 percent, according to Strategy Analytics.

Microsoft could also pose a threat when it releases its tablet software, code-named Windows 8, but this probably won't be until the fall of 2012.

"The ecosystem built around Microsoft is the largest computing ecosystem out there, so this makes it the company most likely to get significant traction in the tablet marketplace," said BGC's Gillis.

Microsoft has said the software will run on a range of devices from traditional PCs to laptops and tablets, and incorporate mouse and keyboard commands. Amazon.com, the maker of the popular Kindle e-reader, is also expected to announce plans to release a tablet this fall, providing a challenge to Apple.

Sebastian forecast sales of up to 3 million units in the first year and said they would eventually outsell other Android-enabled tablets from Motorola and Acer, and could potentially surpass Samsung's Galaxy Tab.

The Amazon offering could be a "game-changer," Colin Sebastian, an analyst at Robert Baird & Co, said in a recent note. The tablet will likely feature Android's Honeycomb OS system, a 7-inch screen and be priced under $300, he said.