Ranked in these QuestionsQuestion Ranking
Pro Drop-down terminal
You can hit F12 (by default, though it's customizable) to open a terminal overlay, Quake-style, as a drop-down from the top of the screen.
Pro Extremely customizable
Guake's appearance is very customizable: from the transparency to the width and height of the window. You can also choose which key to use for toggling the terminal window.
Pro Available in many popular distro repositories
Guake is available in a lot of repositories for the most popular distros. This makes it very easy to obtain and install on almost any system.
Pro Supports transparency
Transparency is particularly useful for when you need to refer to the information displayed by application under Guake window.
Pro Shortcut key F12 can be used to toggle
The global shortcut key, F12, can be used to easily toggle the terminal window.
Pro Tabs support
Guake supports tabs, while working with them is very easy.
Pro Hotkey support
Guake is very fast and easy to open with a customizable hotkey, meaning there's no fiddling with menus or icons.
Con Not cross-platform
Linux only, and additionally targeting GTK3.
Con Not very responsive
Occasionally, Guake slows down and is not very responsive.
Con Does not boot with the system by default
After (re)booting the system, Guake does not boot automatically. You need to open the application and then press the key to make it drop down which is a bit annoying when you want to get started quickly and don't want to press two different keys just to open the terminal.