The Amazon Appstore is officially live (well, in some places in the US at least) and to celebrate, the online retail giant is giving away the brand new Angry Birds Rio game to celebrate.

The give-away is the the first of Amazon's app of the day offerings where, each day, it will be selecting a premium app for Android users to download for nada. Amazon sets its own prices (unlike the official Android Market) so is able to do this, as developers are guaranteed 20% of their listing price, no matter how much Amazon sells it for.

It's this set up that will also see Amazon undercutting Google's official store when it comes to prices as well.

Another killer feature of the web version of the store (it's available as an app for your mobile too) is that you can test drive apps for 30 minutes for free, using a Flash based emulator. Obviously you won't get the full app experience on some apps, as you can't use accelerometers, gyroscopes, cameras and so on - but it will give you a good indication as to what you're buying.

There are around 3,800 apps in the Amazon Appstore at launch, although this number is sure to grow. Don't expect to see many fart-type apps though - Amazon is apparently going to be more selective with the apps that it offers.

And don't expect to see it in the UK just yet - it's all US based for now (with a national roll-out going on now) and we haven't heard anything about an international launch yet.