This looks really nice. I made my own, embedded in my application Springy. It is still very rough, without any drawing optimizations (read: it's slow), doesn't allow free icon arrangement (they are arranged in a grid) and there are a lot more things to improve, but it provides complete browsing functionality (going into items hierarchy), has data source and delegate methods similar to those of NSOutlineView, and also supports bindings. Full drag&drop functionality (including even promise drags) is also already in place. It's still just a proof of concept and I put it into the application just to hear the users feedback and points of improvement that I'd have missed otherwise. Once it's completely finished and polished, it will be publicly available, probably also under BSD license.