As the heading suggests Kaxaml is a open source free xmal editor, it has split xmal and WPF deginer view, but the designer is so far view only all the editing has to be done in the xmal editor part.
You can download this from http://kaxaml.com/
It’s a small 1.7 mb package and comes with some handily features, you can create xaml for both wpf and Silverlight in single window side by side, note that there is no project concept only xmal document can be created and saved. However, it has some fair amount of intellisence.
By the way as no drag and drop feature is still here I would still prefer expression blend over this, and of course visual studio express editions and visual studio professional is far better as far as features are concern.
But for faster editing we can always use the Snippets tab for faster xmal writing. Lots of snippet is given there to help us do fast editing.
Never the less it’s a good tool to play with xaml.