need help finding a "magic" desktop bar

Hi. I am looking for something, and I don't know what it is called. It is a little semi-transparent bar (with a text box) that sits on your desktop. When you type something in it, it will either auto complete and give you the chance to launch it, or just launch it. For example, lets suppose I have Paint installed. I'd simply type "Pa" in that bar, and it would either auto-complete the word and let me launch, or launch Paint as soon as it sees "Pa." The same can be done with URLs, which would be launched in your default browser. It is always on top, and transparent, so it is convinient. I don't know how to search for this. I've tried searching google and this site, and haven't found it. Without knowing what it is called, this is the best description I can give. I'd appreciate any help. Thanks.