GNOME-Do

http://do.davebsd.com/

Free

GNOME Do is fantastic. I’ve got it mapped to the same keys Quicksilver used and it’s just great.

Installation: GNOME App Install

Go up to your ‘Applications’ menu in the top left, click ‘Add/Remove…’. Change the ‘Show’ menu to be ‘All Available Applications’ and then find and check ‘GNOME Do’ and hit ‘Apply Changes’. After installing it, go to the ‘Accessories’ menu under ‘Applications’ and run it. From then on it will have it’s little icon up in your status bar.

To set the hotkey that brings up the window you can type in, right-click the purple icon in your status bar and click ‘Preferences’. A window will pop up- click the middle tab ‘Keyboard’. There you can type the keys you want to use to activate GNOME Do in the ‘Summon’ field.