Until recently Flex developers had the option of using the free, open source SDK (together with a text editor of choice) or purchasing Flex Builder, Adobe’s Eclipse-based IDE for building, debugging, profiling and deploying Flex applications.
The momentum behind Flex and the ever-growing community of developers coming at Flex from different backgrounds means that there is increasing demand for a range of tooling options, some provided by Adobe and some provided by third parties. Over the last couple of weeks we’ve seen JetBrains announce Flex support in IntelliJ, and for .NET developers, Ensemble and SapphireSteel have both released early versions of Flex plug-ins for Visual Studio 2008.
You might think that competition for Flex Builder would be concerning to Adobe, but in fact we see it as great validation of the Flash Platform that others want to invest the time/effort required to create alternative developer tools. As the number of developers adopting Flex continues to grow there will be different sets of requirements and priorities for IDE features – with a range of tools in the marketplace, there will be plenty of room for diversification and innovation in tooling to deliver the features demanded by Flex developers.
In particular, I’m really excited to see the development of Ensemble Tofino and SapphireSteel Amethyst, as one of biggest concerns I continue to hear from .NET developers is that to develop in Flex they have to have to swap between Visual Studio and Flex Builder. Both these tools install as a plug-in to Visual Studio 2008 and, from the information currently available, plan on providing .NET developers with MXML/ActionScript code editing features, application compilation & debugging and Visual Studio project integration in a freely available version.
SapphireSteel, with existing experience in developing a Ruby development plug-in for Visual Studio, have gone further and announced their intention to build a professional, paid-for, edition of their tool. Amethyst Professional, which is due to ship in the 2nd quarter of 2009, will expand on the features in their free version to add an integrated visual designer, interactive debugging experience and full IntelliSense support – making it much closer to Flex Builder in terms of features.
Whilst Silverlight will remain an obvious choice for .NET developers, there is even less reason now to wait for Microsoft to play catch-up on both features and penetration of Silverlight, when Flex enables you to build a Rich Internet Application that can be viewed on 98% of Internet-connected computers without requiring the up-front installation of a browser plug-in. Flex of course also gives you the option of deploying a desktop application that works on Windows, Mac and Linux – something that Silverlight can’t do.
At our recent developer conference, we also demonstrated an early version of BlazeDS and AMF support for .NET – take a look at the current (Java) implementation of BlazeDS to get an sense for the data and messaging enhancements that this will bring to RIA developers using Flex and .NET. More details on this soon…
Andrew Shorten's Blog 
As a long time Flash and .Net programmer I cannot say how great this is. Either of the VS plug-ins coupled with WebORB or the AMF support you mentioned goes a long way to moving Flash Platform development into corporate IT based solely on the Microsoft stack.
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