Gnome Launch Box, an application which is very similar to Quicksilver for Mac OSX, has recieved support for the X server Composite extension. This results in eye-candy in the form of rounded edges and real translucency, making it closer to its OSX “brother”. I definitely suggest that you try it for your self, the screenshots do not fully express how amazing this application looks, and in my opinion it now feels closer to Quicksilver..
sudo apt-get install gnome-launch-box
after installation you may run it by pressing alt+f2 to bring the run dialog box and typing:
If you want it to startup everytime you logon then add the entry is system > prefs > sessions. in the startup programs page click “NEW” button. type anything in the ‘Name’ field and in the ‘Command’ field type:
For other distros : GNOME Launch Box | Imendio Developer Pages