Amazon's Appstore doesn't have the sheer size or name recognition of Apple's App Store or the Google Play store, but as Amazon's tablets grow in popularity, the Appstore is quickly becoming a contender in the category. How quickly? Amazon announced today that downloads in the store have increased 500% since last year.

Amazon tablets like the Kindle Fire and Kindle Fire HD run a version of Google's Android OS, but it's highly modified. Only apps customized for the Kindle Fire and sold in the Amazon Appstore can run on the device. Non-Kindle-Fire apps are also sold in a version of the Appstore available for Android tablet owners.

If it continues to grow traction with users and developers, Amazon could use the Appstore to upset the app market in a similar manner to how it revolutionized books and retail. That's potentially good news for customers, and potentially scary news for Apple and Google.

[via GigaOM]