The new Ubuntu HUD resembles a product Aza Raskin developed a while back for Windows. It’s called Enso Launcher and has similar functionality. Besides launching apps it could control apps, manipulate text and do simple calculations as is shown in this screenshot.
A similar feature exists in Mac OS X and it’s especially helpful when controlling a Mac with a keyboard. It works and looks similar to spotlight. To use it, hit the following key combo and start typing:
Command + Shift + /