self-published almost all of the later ports of the game, with the exception of the PSP version, which was produced under license by Abstraction Games. When Rovio began writing new versions of the game for other devices, new issues came to light. As the team began working on a version for Android systems, they observed a large number of configurations of device types and versions of the Android software. The number of combinations of software version, processor speed and even user interfaces was significantly larger than that for the iOS version. Ultimately, the team settled on a minimum set of requirements, even though that left nearly 30 types of Android phones unable to run the game, including some newly released phones. It was released on October 15, 2010. One month after the initial release on Android, Rovio Mobile began designing a lite version of the game for these other devices. In early 2010, Rovio began developing a version of Angry Birds for Facebook. The project became one of the company's largest, with development taking over a year. The company understood the challenges of transplanting a game concept between social platforms and mobile/gaming systems. In a March 2011 interview, Rovio's Peter Vesterbacka said, "you can’t take an experience that works in one environment and one ecosystem and force-feed it onto another. It's like Zynga. They can’t just take FarmVille and throw it on mobile and see what sticks. The titles that have been successful for them on mobile are the ones they’ve built from the ground up for the platform." The Facebook version incorporate social-gaming concepts and in-game purchases and entered beta-testing in April 2011; the game became officially available on Facebook in February 2012 as Angry Birds Facebook (later Angry Birds Friends). Improvements for the game include the ability to synchronize the player's progress across multiple devices; for example, a player who completes a level on an Android phone can log into their copy of the game on an Android tablet and see the same statistics and level of progress. Release The initial iOS version of the game included a single episode entitled "Poached Eggs", which contained three themed chapters, each with 21 levels. From time to time, Rovio has released free upgrades that include additional content, such as new levels, new in-game objects and even new birds. As updates have been released, they have been incorporated into the game's