Flex, the Adobe tool for delivering Flash applications that mixes ActionScript and an XML page layout language, will be completely open source by the end of 2007, with much of the code available now.
With Flex at the heart of Adobe's Apollo rich internet application platform, this release marks a significant change in Adobe's traditionally proprietary approach to development tools and frameworks.
Adobe will be using the Mozilla Public License for Flex, and the opened code will include the source of the Flex SDK's ActionScript libraries, along with the Java source of the Flex compilers and the debugger (see here for the actual announcement).
That's everything you'll need to write a Flex application (minus the Flash Player, which remains firmly Adobe). It's also everything you'll need to write your own development environment, as the Eclipse-based Flex Builder IDE is remaining closed.
Adobe senior principal scientist Mark Anders described the announcement as helping Adobe "reach a new set of developers", and giving the Flex development community "a bigger voice in how we move Flex forward". Adobe will be hosting the project, with the Flex development team contributing while still working on the company's commercial Flex projects and development tools.
Recently there's been criticism of Adobe's dominance of the web development marketplace, but this announcement should go some way to allaying these fears. An open source Flex, along with the work Adobe and the Mozilla Foundation are doing with the Tamarin ActionScript compiler (a key Flash technology), means Flash-based web applications will be able to be developed in any IDE and on any platform - and in the case of Flex, delivered from any web server. ®