Everyone knows about Apple’s iOS and the Google Play store, but there’s another application marketplace that’s growing extremely quickly.

Amazon today announced that total app downloads in its Appstore have grown more than 500 percent compared to 2011. During the third quarter alone, the number of developers who have incorporated in-app purchasing has doubled.

Amazon didn’t share exactly how many apps are available in its store and failed to provide the number of downloads. Still, that the marketplace is growing that rapidly is notable, if not surprising.

Amazon’s Appstore launched in the U.S. in 2011. Earlier this year, the company expanded its footprint to Europe, and recently brought it to Japan. The marketplace was initially designed for third-party Android devices, but with last year’s launch of the Kindle Fire, also included support for Amazon’s slate.

When it comes to mobile apps, the Appstore is typically an afterthought, if it’s even mentioned at all. Apple’s App Store, which launched all the way back in 2008, is the only way iOS users can get programs onto their products, so naturally that marketplace gets some attention.

Google Play, meanwhile, is the search giant’s application store, catering to any Android-based device. The Google Play store is widely regarded as the most popular Android marketplace, earning its crown by being bundled across the Android-based devices that launch worldwide.

It’s impossible to say, given that, that Apple or Google will ever be beaten in the application space. After all, both marketplaces have well over 700,000 applications, and billions of apps have been downloaded. Amazon, despite its growth, will need years before it will be able to match that.

But the fact that the application store is growing so rapidly is rather interesting. There seems to be a general sense in the marketplace that because the App Store comes bundled in the iPad and iPhone, and the Google Play store is readily available on Android products, Amazon’s Appstore, which comes bundled in just a handful of devices, should be ignored.

But if Amazon’s figures are to be believed, that’s no longer the smart move. Amazon has found a way, despite all of the odds, to carve out a portion of the application market for itself. Developers are increasingly finding that the company’s store is worth trying out, and as more Kindle Fires are sold, Amazon customers are finding things to like, as well.

The application market is an odd place. Although in most markets around the technology industry, when one company’s product grows, another’s declines, that’s not true in apps. The world is increasingly warming to applications, and high tide is swelling. It’s possible now for the App Store and Google Play marketplace to grow, and at the same time, for the Amazon Appstore to succeed with them.

Call it good timing or a sound business model. But whatever it is, Amazon’s strategy with the Appstore seems to be paying off.