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?
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.
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.
for windows,try RocketDock
Maybe not a classical dock-app but I think the True Launch Bar is a very good replacement and/or add-on for the windows task-bar. You can configure the bar in nearly every manner you want (look also at the screenshots on the homepage for examples).
And it also works under Windows 7.
Cairo-Dock (also called GLX-Dock) is my favorite dock. To install it, type this in to the terminal:
$ sudo apt-get install cairo-dock cairo-dock-plug-ins cairo-clock
When it's done installing, click the Ubuntu menu and type in Cairo-Dock. Click the "CD" icon and Cairo-Dock should start up.
Did you know that Cairo-Dock is the only dock that supports sub-docks? It's also the most configurable dock available for any operating systems. Too bad it runs only on Linux!