On April 26, Adobe announced strategic plans to move the development of Flex to an open source model.
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Adobe To Open Source Flex (Press Release at Adobe.com) Overview
Adobe is announcing plans to open source Flex under the Mozilla Public License (MPL). This includes not only the source to the ActionScript components from the Flex SDK, which have been available in source code form with the SDK since Flex 2 was released, but also includes the Java source code for the ActionScript and MXML compilers, the ActionScript debugger and the core ActionScript libraries from the SDK. The Flex SDK includes all of the components needed to create Flex applications that run in any browser - on Mac OS X, Windows, and Linux and on now on the desktop using “Apollo”.
Developers can use the Flex SDK to freely develop and deploy Flex applications using either Adobe Flex Builder or an IDE of their choice.