Amazon officially opened its new and much-anticipated Android app store today.

Serving up a round of competition to Google's Android Market, Amazon's Appstore for Android is stocking almost 3,800 apps for starters, with more on the way. To kick off the store opening, Amazon is giving away a free copy of Angry Birds Rio and is promising to offer one paid app for free each day.

But the Amazon shop is opening amid controversy. Apple yesterday sued Amazon over the use of the term "App Store," for which Apple filed a trademark after the release of the iPhone 3G. Apple is contending that use of the term could "confuse and mislead customers." Lawyers will surely make note of the fact that Apple uses the term as the two-word phrase "App Store," while Amazon has tweaked it slightly to the one word "Appstore," perhaps in an attempt to distinguish it.

Amazon's launch of its Appstore for Android comes at a time when Google's own Android Market has been facing some challenges, notably in the area of security. Google recently was forced to pull 50 different malware-infected apps that were masquerading as legitimate programs, calling into question the processes that the company uses to allow apps in its mobile store.

Before shoppers at Amazon's Appstore can download Angry Birds or other apps onto their Android devices, they'll first need to install the retail giant's Appstore app on the device, a process explained on the Getting Started page. Once the Appstore app is installed, people can then browse and search for titles throughout the store. An Amazon acccount is also needed to download apps.

As with most app stores, Amazon has organized its titles into a wide array of categories, including games, education, news and weather, travel, shopping, and social networking. Users wil also find apps in special categories, such as bestsellers, new releases, and free apps. Each app offers full descriptions and details along with user reviews. Amazon will also recommend certain apps based on a person's interests and history.

Clicking on the "Buy App" or "Get App" button will download an app and add it to the My Apps page on the Web site or install it directly on the mobile device. People can browse, download, and buy apps either from their PCs via the full Web site or through the Appstore app on their devices.

Amazon is also offering a "test drive" feature for many apps through which people can try before they buy. The Test Drive option lets users launch an app on Amazon's cloud-based EC2 service to get a quick feel for how it works.

The Appstore for Android is generally compatible with any device running Android 1.6 or higher, according to Amazon. But there seems to be an issue with Android devices from AT&'T. Amazon says that AT&'T smartphone and tablet users can't currently install the Amazon Appstore app or buy apps from the store. The company says that AT&'T is working on the issue and suggests that users visit the AT&'T Web site to be notified when they can use the store.