Flex Builder is a set of extensions to Eclipse. Those extensions are not open source. That said, the compiler is part of the Flex 3 MPL license and there are numerous third party, free and/or open ways to code Flex apps, so that part of the stack is open, with options to use non open software just at IntelliJ Ideas or even Adobe Flex Builder.

The VM in the Flash Player (Tamarin) for both desktop (and now mobile, as of last night) is also free as in speech and hosted by Mozilla. The rest of the Flash Player is free as in beer, but not open.

HTH,
David
Adobe

Maybe too hard to split on versions, but the Flex 2 SDK seems to have a pretty restrictive license, with no modifications or reverse engineering (see 2.10.x in the Adobe Flex 2.0.1 SDK License you have to accept to download). Version 3 moving to MPL is certainly good news, as is the impending LGPL of the BlazeDS and AMF spec.

Are there still other parts of the Flex stack that remain proprietary, or are the Builder and the Flash player the only remining bits?

So, I would say that you should probably move Flex to the open source side of your slide. Keeping AIR and Flash on the proprietary side would be accurate.

Mike

Mike Potter
Adobe Flex Team

BlazeDS is available.

This press release says that:

. . . the technologies included in BlazeDS, along with the Action Message Format (AMF) protocol specification, are being contributed to open source under the Lesser General Public License (LGPL v3), and are available immediately as public betas on Adobe Labs.

But it looks to me like in downloading BlazeDS beta you have to accept a terms of use which is certainly not LGPL.

Returning to the press release, I saw this at the end:

Subscription pricing will be announced at the time of general release of BlazeDS under the LGPL v3, currently scheduled for early 2008.

So it will be LGPL at some point, but for now it is only free as in beer.