Amazon opened its Amazon Appstore for business on Tuesday morning, and in a bid to bring in Android users, it's giving away a free download of Angry Birds Rio for Google's OS.

Normally, Angry Birds Rio would have a price of 99 cents, but Amazon is looking to lure Android owners to its online storefront by offering a different paid app for free each day.

For the store's day, Angry Birds Rio is the free app, but it may or may not remain free beyond its debut, said Aaron Rubenson, category leader for the Amazon Appstore.

And so far, Angry Birds Rio for Android is exclusive to the Amazon Appstore (The iOS version is available in the Apple App Store and iTunes for 99 cents).

Amazon is hoping its Appstore, which currently sells only Android apps, will challenge Google's Android Marketplace as the main spot to get applications for Android phones and tablets.

The Seattle-based online retailer is also slowly rolling out a unique "Test Drive" feature for many apps sold through the Amazon Appstore over the next few days, Rubenson said.

If an app has a Test Drive available, users will be able to launch a demo version of an app, running on Adobe Flash within a user's Web browser. The demo will allow them to try the app before buying it, though the demos will be limited and won't replicate certain phone features such as an accelerometer or a camera, Rubenson said.

On day one, Amazon has about 3,800 Android apps available for download, each of which have been tested and approved by Amazon employees as virus-free, an effort Amazon has been working on since January, when it began taking submissions to the Appstore.

And although the Appstore launched Tuesday, squarely in competition with the Android Marketplace, it also opened amid legal gripes from Apple.

Last week, Apple filed a suit against Amazon over the Amazon Appstore name, arguing that it's too close to Apple's App Store, which sells apps for the iPad and iPhone in its iOS operating system.

Amazon launched an Amazon Appstore app for Android devices as well, which allows users to download apps from the retailer directly on their Android phones or tablets.

App purchases will be made using the same Amazon account consumers use to buy books on Kindles and other items on Amazon.com.

For each Android app sold through the Amazon Appstore, Amazon will take a 30% cut of revenue, the same cut the company takes for e-book sales.

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-- Nathan Olivarez-Giles

twitter.com/nateog

Upper images: Screenshot of the Amazon Appstore on Amazon.com. Credit: Amazon

Middle image: An Android app sold on Amazon with a Test Drive option. Credit: Amazon

Lower image: The Test Drive feature in action. Credit: Amazon

It's Angry Birds, complete with the little green pigs and collapsible blocks, but this game isn't found on a smart phone or a tablet.

It's a cake. A playable Angry Birds birthday cake (as seen in the video above).

Using a slingshot, players can hurl icing-covered not-so-happy birds toward pillars and planks stuck in frosting, replicating the play of the smart phone and tablet game itself.

The Angry Birds cake was baked/built by Mike Cooper, one of the writers at the tech blog Electricpig.co.uk, for his son Ben's sixth birthday.

Cooper also wrote a step-by-step tutorial on how to make the dessert.

The game company behind Angry Birds, Rovio, tweeted about the project, saying, "Very cool! Might be the first playable Angry Birds cake ever."

Cooper wrote in a blog post that baking outlandish cakes for his children has become a family tradition, and his son is a huge Angry Birds fan, hence the project.

"With my little boy Ben turning 6 years old over the weekend and appreciating his love of Angry Birds, I thought I'd have a shot at making him a playable Angry Birds birthday cake with working catapult and iced birds as ammunition," he wrote. "It took 10 hours to make and 2 minutes to destroy."

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-- Nathan Olivarez-Giles

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Video: Playable Angry Birds birthday cake. Credit: Electricpigtv via YouTube.

Angry Birds' Super Bowl ad this Sunday will be the first to be broadcast with an embedded code.

The code will unlock a secret level in the Angry Birds game, normally inaccessible to players, according a report from Reuters.

The 30-second commercial will spotlight the upcoming Angry Birds Rio game app for smart phones and tablets, developed by game company Rovio, which is hyping the upcoming Fox animated movie "Rio."

The Angry Birds Super Bowl ad is set to run during the fourth quarter of the matchup between the Green Bay Packers and the Pittsburgh Steelers, being played in Cowboys Stadium in Arlington, Texas.

The game, Super Bowl XLV, is airing on the Fox Broadcasting Network.

The unlockable level will also take Angry Birds users to a Rio sweepstakes, which features a prize of a trip to the "Rio" movie world premiere in Rio de Janeiro, Brazil, on March 22 -- the same day the Angry Birds Rio game launches, Reuters said.

The "Rio" movie hits theaters April 15.

For those who miss out on the commercial and the special level game code, the ad will be posted on YouTube after it airs, the report said.

The news of the Super Bowl ad and the embed code was first announced by Advertising Age, Reuters said.

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-- Nathan Olivarez-Giles

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Image: Angry Birds Rio game app advertisement. Credit: Rovio