What is a good app for Ubuntu that mimics RocketDock?

I'm looking for a dock application to use on Ubuntu, but suggestions are welcome for all platforms. I'm familiar with RocketDock, but don't think that it works for Linux. Any ideas?

From MakeUseOf -- 8 power Docks for Linux.
This BrightHub posting is on similar lines (so is this older link).

Avant seems to be the pick.

Avant Window Navigator (Awn) is a dock-like bar which sits at the bottom of the screen. It has support for launchers, task lists, and third party applets. The official applet and plugin repository is in a separate project, awn-extras.

If you are using Ubuntu Hardy and above, AWN is included in the repository.

Cairo Dock was my personal favorite:

To install via apt:

sudo apt-get install cairo-dock cairo-dock-plug-ins

GNOME Do has a skin called docky that works a lot like RocketDock. Do is also a good replacement for the Windows app launcher Launchy.

I like ObjectDock for Windows. The free version should be enough for you, but in case you want more (like tabs), there is a paid version available for only $20.