QuickSilver from BlackTree Software is a AMAZINGLY GREAT launcher for the Mac. It's a three pane launcher for the Mac that I've been using for about six months. In short, a three pane launcher allows you to launch apps or use simple sentence based commands to do all sorts of system tasks. (Like sending an email, or multiple image resizes) I am at the point where it is almost indispensable. And so I began to wonder if something similar might be available for other operating systems as well.
And yes there are. There are a few three pane launchers for Windows. Shuriken is the I've found so far. (Launchy is great to, but it's not really a threepane launcher. Also, haven't tried it yet, but there is Gnome Do for Linux (despite the name it supposedly works on KDE as well).
Finally, while not a three pane launcher (or an OS extension) I think it's important to highlight Mozilla Labs Ubiquity for Firefox. Ubiquity brings Sentence Based language to the Web Browser. I'm still looking further into how to best use it.