A combination of a matrix console screensaver and a console security tool.
http://mixter.void.ru/misc.html
http://www.asty.org/cmatrix/
CMatrix is a program I wrote one evening because I didn't want to have to run Wind*ws to see the cool scrolling lines from 'The Matrix', my fave movie.
Cmatrix is written in ncurses under Linux, and should compile on other OSes with few modifications. I am always interested to hear from people who use this program and any modifications they make to it!