There are quite a few terminals out there, and some of them follow the drop-down style. GNOME has Guake, a GTK-based terminal emulator with lots of features, but there is also Tilda or Final Term, while the KDE de-facto terminal is Yakuake.
Drop-down terminal applications have the advantage that they can be shown or hidden using a single global hotkey, and they usually make it easy to resize their size, change the time of the drop-down animation, keep it on top of other applications.
