Someone's taking all the rumors about Apple introducing a tablet/slate computer/digital reading device pretty seriously.

On Wednesday, Amazon.com more than doubled the royalties it offers authors and publishers using its Kindle self-publishing system.

Today, the Seattle company went after Apple developers and others building applications for mobile devices, opening up the Kindle to outside developers and providing them with a new Kindle software developer kit.

"We've heard from lots of developers over the past two years who are excited to build on top of Kindle," Ian Freed, Amazon Kindle vice president, said in a release. "The Kindle Development Kit opens many possibilities -- we look forward to being surprised by what developers invent."

Early participants include games giant Electronic Arts, which Apple has used in the past to show off the gaming capabilities of the iPhone and iPod Touch.

Other applications being developed now include a Zagat guide and casual games from Sonic Boom. Amazon said the applications will be available in the Kindle store "later this year."

Apple hasn't said anything yet about the tablet computing device it's expected to announce on Jan. 27, although its success would depend on Apple's ability to make it an attractive platform for software developers whose applications were key to the iPhone's success.

Among all the stories speculating on Apple's device, the definitive one so far is today's piece in the Wall Street Journal that describes how the company's been talking to book publishers, newspapers, magazine publishers and movie and TV companies about getting content onto the device (including media conglomerates such as News Corp., the WSJ's parent company ...). Its sources say the device will have about a 10-inch diagonal screen and cost around $1,000.

The device may also have some of the standard applications that come with touchscreen PCs such as "sticky notes" for posting messages on the shared device.

One tidbit in the WSJ story that stood out was Apple's plans to offer an online version of the iTunes store that it would proliferate with "buy this song" type buttons that could be added on all sorts of Web sites - replicating Amazon's online store and affiliate program.

Amazon has long worked with Web developers who use its commerce and online computing platforms, but it has been obsessive about controlling the Kindle and the experience it provides to users.

Today's announcement suggests the company's not opening up much -- it's limiting access to the Kindle developer kit and imposing various controls on its usage, which won't help woo iPhone developers. From Amazon's release:

Starting next month, participants in the limited beta will be able to download the Kindle Development Kit, access developer support, test content on Kindle, and submit finished content. Those wait-listed will be invited to participate as space becomes available. The Kindle Development Kit includes sample code, documentation, and the Kindle Simulator, which helps developers build and test their content by simulating the 6-inch Kindle and 9.7-inch Kindle DX on Mac, PC, and Linux desktops.