Adobe has announced that a large portion of the next version of Flex goes open source under Mozilla Public License (MPL). Here’s the partial list of what becomes open: mxml, compc, and ActionScript compiler, command line debugger FDB, Flex framework and RPC libraries and testing infrastructure.

These are some of the components and tools that will not be open sourced: Flex Builder, Charting components, Flash Player, Apollo.

This is a step toward creating a wider Flex 2 market. The interest to rich Internet technologies grows leaps and bounds, and Adobe Flex is one of the leaders in this league. There is already a decent number of developers who are interested in Flex and Adobe hopes that open sourcing Flex will bring more developers on board.

The source code of the Flex framework was available all the time, but the developers could have improved it by extending these components. But now they will be able to improve the original components as well.  

Another good thing is that the third-party component developers will be able to include Flex compilers into their components. To the best of my knowledge, MPL will allow third parties distribute their own components under any other licenses as long as the original Flex code stays under MPL. The Web tier compiler is a gray area though – it’ll be open sourced for Apache containers and Microsoft IIS. I was not able to get a clear answer if the third-party developers will be able to include Flex Web compiler into components deployed under commercial J2EE servers.  

Adobe will still govern the modifications of the Flex libraries – they’ll set up the repositories for the Flex source code, will set up builds, etc.

I believe that open sourcing Flex will draw attention of some serious developers to the new kid on the block. The Flex team may become substantially larger.