I got in at around 6:30 a.m. Chicago time…though it appears it may have been open five hours earlier based on the countdown clock for Angry Birds Rio.

The appstore features a free version of Angry Birds Rio for Google’s (GOOG) Android. Amazon will offer a regularly paid app available for free every day. And Apple has already welcomed its rival— with a lawsuit.

The store at amazon.com/appstore lists 100 apps initially in six categories, including Games, Utilities, Entertainment, Social Networking, Music and Productivity.

I spotted three versions of Rovio’s Angry Birds, more than enough to numb your brain and escape reality permanently. There were also many other familiar apps already available in the Android Market.

Chuong Nguyen reports in Gottabemobile: “The Amazon-branded third-party app store will rival Android’s native Google Android Market on most Android devices. In addition to carrying third-party Android titles, Amazon is looking to differentiate its model from Android Market by offering lower prices on select apps and exclusive titles. Apps sold via Amazon Appstore will come with Amazon’s DRM mechanism and will also make it easier for consumers to re-download digital titles, much like what Amazon has done for e-books via the Kindle bookstore.”

Brian X. Chen reported in Wired: “First leaked in September, Android app store will be a curated market, meaning Amazon reviewers will determine which apps are allowed inside, similar to Apple’s iTunes App Store. That’s a contrast to Google’s ‘anything goes’ policy for apps that appear in the Android marketplace.”

He said his sources told him customers will be able to purchase apps through the Amazon.com website or directly through a native Amazon app on their Android devices.

Because Amazon and its payment system are so widespread internationally, Chen said it threatens not only Google, but Apple’s iTunes.

Meanwhile, the Apple gods were angered. So they sued.

Edvard Pettersson and Don Jeffrey reported in Bloomberg that Apple filed suit against Amazon  for trademark infringement on use of Amazon Appstore. Apple of course has its own “App Store.”

Apple has had a hit with App Store, celebrating the download of its 10 billionth download recently.

But Apple doesn’t want to share…at least the name.

Bloomberg said: “Apple, in a complaint filed March 18 in federal court in northern California, accused Amazon.com of trademark infringement and unfair competition and asked for a judge’s order to prevent the company from using the ‘App Store’ name, as well as for unspecified damages.”

Apple said Amazon unlawfully used the name to solicit software developers as well as in the download service. Or can we call that a market.

“We’ve asked Amazon not to copy the App Store name because it will confuse and mislead customers,” said Kristin Huguet, a spokeswoman for Apple.

Amazon was mum.