Have you ever been in need of a console terminal, but thought that switching windows is not smart enough for you?
I think that need is the mother of invention. Since I use GNOME I always wish for some application in GTK that are already in QT/KDE. But I'd rather use GTK so, why not just create my own drop-down terminal?
Guake follows the same line of Yakuake and Tilda, but I am trying to meld the best of them into a single GTK-based application.
Guake has been written from scratch. 

In a nutshell, Guake is a drop-down terminal for Gnome Desktop Environment, so you just need to press a key to invoke him, and press again to hide.