ruby

A week ago, I was introduced to Visor, a utility for turning the Mac OS X console into a "Quake-style" console. What does that mean? In a nutshell, it means that the terminal runs not as a normal window, but as a boderless window attached to the top of the screen. Hit a button and the console slides down. Hit the button again (or unfocus from the window) and up it slides. It's a convenient way of keeping a terminal accessible at all times. (And, yes, it supports multiple tabs.)
Visor: "Official" screenshot

Visor is written in Ruby, and is easy to install (though the installation process is a little more, ahem, manual than your typical Mac OS application.

Tip: By default, Visor slides away when the window loses focus. Sometimes, though, it is desirable to keep the visor down for short (or perhaps long) periods while working in another window. To do this, expand visor and then click on the visor terminal icon on the right side of your menu bar. Select "pin" and the visor will stay open. To set it back to its regular behavior, select "unpin".

Thanks to sdboyer for turning me on to Visor.