Cairo dock is a Mac OSX dock-like application that you can install in your Linux machine. One of the advantage that it has over other docks is that it does not require any compositing window manager to work. Even on a low-end PC, it will still work fine. This is not possible for docks like Avant Window Navigator which depends on compositing manager (such as Compiz) to function.
If you are using a PC that does not support any compositing manager, or you wanted to try out alternative dock for your Ubuntu machine, follow this tutorial to install and configure Cairo Dock on your Ubuntu Intrepid.