Amazon has launched Amazon Underground, a whole section of its appstore that offers completely free Android apps to download.

They are full versions of thousands of games and other applications that, on other devices, might contain in-app purchases, but through Amazon Underground, even the in-app content is free.

Everything available in the Amazon Underground section of the store is "actually free" and labelled as such and won't cost you a single penny now or in the future. And if you think that it must be games that wouldn't otherwise be popular, think again.

Currently available are Sonic CD, Castle of Illusion Starring Mickey Mouse, Goat Simulator, OfficeSuite Professional 8, Sorcery!, and many more. What's more, this is not just a promotion, it will be an ongoing incentive to Android owners.

Fire HD and Fire HDX tablet owners also get access to the apps automatically.

Amazon is paying developers itself on a minute played basis. So the more you play the games or use the apps, the more they will be paid. This allows the apps to remain free and for developers to technically make money that they would otherwise accrue through in-app purchases. Everybody wins. Well, that's the idea anyway.

So how do you get Amazon Underground?

Well, thanks to Google's rules about offering apps on Google Play that give access to other apps or games, you have to download it separately and install manually.

To get the portal application, head to using a browser on your Android phone or tablet.

Then, once past the introduction letter that pops up, click the download Amazon Underground button. This will then download the APK file needed to install the app.

Before installing, you will need to head to your device's "settings" and then "security". Turn on the slider next to "unknown sources" to allow installation of apps from unknown sources.

Head back to your overall app screen and head into your download folder. Tap on the Amazon_App.apk that has appeared there and choose "install". The app will install and when you next open it, after logging in with your Amazon account, you will see a section called "Amazon Underground" which lists all the "actually free" games and apps you can download. Bingo!

Now, if only someone did this for iOS. Ah well, we can but dream.