First I checked my calendar to make sure it's not April 1st... but no, Adobe is actually going to open source Flex! The blogosphere is already full of it.
From the release: "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'."
Also here are two video interviews with members of the Flex team. I need to digest this now, I'm blown away - there's just too much happening at the moment and I feel there's more to come. Whatever next - AMF? RTMP? How long before Microsoft copies the move? ;-)