GeekTool is a System Preferences module for Mac OS X Panther (10.3) or Tiger (10.4) to show system logs, unix commands output, or images (i.e. from the internet) on your desktop (or even in front of all windows).

Why is this cool?

Well, instead of having to dig through console to see who's actively hitting your secure.log or system.log, you can either tap these logs directly, or put a small looping tail script together for concatenating your favorite logs and giving you a play by play on your desktop.