Do you want bottom dock like in OS X or elementary OS? If you are using GNOME Shell, then Dash to Dock by michele-g is the right extension for you. It helps you to turn the original left-vertical panel in GNOME Shell overview into a dock and control it freely. You even can put the dock in any position of your screen by this extension.

Formerly, DockbarX is a Gnome2 taskbar applet, AWN Applet, Mate taskbar applet and stand alone dock with groupping and group manipulation. Now, DockbarX can be used as a panel plugin for XFCE panel. With this application, Xubuntu users - like me - can get an icon only application launcher, grouping ability, theme supports, pin application to panel and more!

Plank Dock is a simplest dock application on the world. Its goal is to provide just what a dock needs and nothing more, which means its provides the very basic dock application functionality: launch applications and switch between running applications. Plank Dock is built under Docky technology but without fancy things like docklets, painter and even settings dialog.

Cairo Dock is an dock bar application which brings animated and beautiful app launcher to your desktop. It can run on GNOME, KDE, and XFCE desktop environment.