It is compatible with XP or Vista, and sits at the bottom of your screen. Due to this, it works best if your toolbar is moved to on side, and unlocked so it hides away. The Xwindows Dock is unmovable, which is a shame as the OSX version is not. It is attractive, well animated, and is highly customizable.
Like the OSX dock, Xwindows Dock features stacks, which is a cool way to view often used folders. Instead of opening a folder window, the contents pop up in a stack, and close when you click away from the window. On Xwindows Dock this works well, although if you stack a folder with many different icons in it, the effect on the dock is a bit ugly. Overall, this is a great OSX dock clone. It's not quite as slick as the original, but for a free application it's very hard to complain.

OS: XP/Vista/7