I have been working on an SVG editor, written in Cocoa. A lot of the
basic rendering features are working now. It's intended to be a stand-
alone editor as well as something that can be embedded in other
applications.
I chose SVG because I was looking for something to use in the next
major version of my icon editor (Icon Machine), and SVG includes
pretty much all of the primitives and effects that I use in Photoshop
when I make my own icons. It's also pretty well-defined, including a
test suite to help me make sure my rendering is correct.