Avant Window Navigator is a dock for the Free Desktop which shows your launchers and open applications. It also contains support for extensions, via plugins for third-party applications, which communicate with the dock with DBus, and via applets, which allows for workspace switchers, system trays, clocks, etc., to be embedded in the dock. These applets can be written in C, Vala, or Python.
Awn currently requires compositing support in order to run. Window managers which support compositing include (but are not limited to) Metacity (part of GNOME), Xfwm4 (part of Xfce), KWin (part of KDE4.x), and Compiz. There are also standalone compositing managers, for window managers without support built-in: Cairo Compositing Manager and xcompmgr.