Cockatoo is perfect if you're one of those who uses iTunes to listen to music. It provides a much simpler way of managing it, leaving you to do other things on your Mac. Sure, you can control iTunes from its interface and also from the Dock (right-click the iTunes icon), but this just isn't suitable for all users.
Cockatoo quietly waits for you at the left or right border of the screen without occupying any space. You only need move your mouse to the edge to have all your music before you.
Note: Now requires OS X 10.10 or later.