Leaving Ubuntu and switch to the Mac’s world has been a pleasant experience because of the beautiful yet effective operating system. Snow Leopard is my favourite development platform now along with Slackware Linux. I’m working with the terminal all the time and love they way Guake doing in Gnome or Yakuake doing in KDE, simply pressing a shortcut key & the terminal will slide through the top edge, ready for use all the time. I found this so handy that I couldn’t live without it.
So searching for a similar solution, it all come down to Visor
Visor is a system-wide terminal accessed via a hot-key of your own. Installation and download instruction you can take from its homepage.

Have fun!
Links: http://visor.binaryage.com/

