Source : http://weblog.mrinalwadhwa.com/2008/05/09/a-list-bloggers-confused-about-rich-internet-application-technologies/

Microsoft Silverlight is equivalent to Adobe Flash Player and Adobe Flex framework taken together

Sun’s JavaFX is equivalent to Adobe Flash Player + Adobe Flex Framework + Adobe AIR + some more yet to be done stuff in the mobile space

JavaFX Script is a programming language like Adobe’s ActionScript+MXML … or Microsoft’s XAML+any CLR language

Adobe’s FlexBuilder is an Integrated Development Environment like Microsoft’s Visual Studio or Sun’s NetBeans

Microsoft’s Expression Blend is an RIA design tool which has no equivalent yet .. Adobe is building Thermo which will fill this gap on their RIA stack .. and apparently Sun is doing something in this space too.