Amazon is testing out a new ebook service called "Kindle Unlimited." As spotted by GigaOm this morning, the service offers a large number of ebooks and audio books for $9.99 a month. Most of the Kindle Unlimited test pages were taken down this morning after users began to notice them, but according to Amazon the subscription service will offer over 600,000 ebooks and "thousands" of audio books.

This is a separate offering from the lending program the company already offers. Kindle owners with Amazon Prime memberships are allowed to borrow 1 book per month, but there isn't any clear indication on whether or not the content available will vary between the two services. At this point, there are only minor differences in the selection the two offer.

According to reports, many of the books are from Amazon's publishing imprints and available on the aforementioned Kindle Owners Lending Library, including popular titles like the Harry Potter Series.

Rumors surfaced again last month about Amazon creating a book lending service to compete with similar services, and this appears to be the early stages. However, unlike its competitors Scribd and Oyster, Kindle Unlimited doesn't look like it will offer content from the big five publishers: Penguin Random House, Simon & Schuster, HarperCollins, Macmillan, and Hatchette. 

Amazon appears to have moved the service back into hiding for now, but you can check out a preview of what's to come via Google's cache of the page.