Adobe has open sourced a couple libraries they’re working on called Adam and Eve. From my brief skim through the overview, both libraries essentially sound like they aim to provide a cross platform architecture that is somewhat equivalent to what Avalon is going to deliver for Windows. Adam, for example, sounds somewhat like the DependencyObject + DependencyProperty + Expression features of Avalon. Eve defines a syntax (like XAML, but not XML) and a layout engine. They’re already talking about an Eve2 where they separate the syntax from the model so that other syntaxes can be leveraged to create an Eve object graph. In other words one could write a basic XAML parser that constructs an equivalent Eve object graph. Or, even more useful, one could write an HTML parser that constructs an Eve object graph.