ubuntu 12.04 - 12.10

To add Guake to the Unity system-tray, you need to add it to the system-whitelist

Using dconf-editor (installed using the dconf-tools package), navigate as shown and add guake to the whitelist.

You then just start the app via guake & to make it appear in the system tray.

Make sure your guake properties (guake -p) has the system tray checkbox ticked:

13.10 and later

The ability to whitelist applications has been removed from Unity.

The argument the developers have is that applications should have been updated to support Ubuntu indicators.

There isnt a direct method to-do this without adding an additional PPA.

sudo add-apt-repository ppa:gun101/ppa

sudo apt-get update

sudo apt-get install guake-indicator

Search for "Guake indicator" in the dash to start the app-indicator