it allows you to use terminal when and where ever you need it,
it has a cool animation that scroll (the terminal window) down from the menu bar (like a console from within 3D games when you press ~ key),
of-course it needs the terminal application to be running, and you use the key combination Ctrl+F1 (can be changed), in order to install it you will need SIMBL which is a smart simple way to write small plugins to existing application (without compilation or ever needing the application source).
the screenshot at the top of the post display the way the end result looks like, and here is a small video that display the animation.
in order to install it follow these steps:
1. Download SIMBL from here
2. Install SIMBL (execute the downloaded SIMBL.pkg)
3. Download Visor from here.
4. copy the downloaded Bundle file into: ~/Library/Application Support/SIMBL/Plugins
if this folder does not exist - create it
5. launch (or relaunch) the terminal application and press Ctrl+F1
Note the "Visor Preferences..." menu item from the Terminal Menu.