Mail and many other programs have been using this new kind of split view for a long while now. It typically has a main content area on the right side and a long table or outline view on the left side with a strip of a handful of buttons to add a new object, perform actions on it, and whatever else. Here’s an example of it seen in Araelium Edit:

Writing the code to create this kind of view is fairly trivial if you know what you’re doing, but why bother reinventing the wheel? I give you AGShelfView.

Use this in combination with AGSidebarView and you’re off and running with a pretty slick looking little window. You can also customize this view further adding a subview with animation. For example, check out this little movie:

Download the AGShelfView Code