LOCKME

Lockme is a very simple yet powerful utility for your macintosh. Lockme, upon your command, blacks out the screen and displays a moving "Enter Password" dialog.

Immune from force quits, without any nasty INITs or background apps Lockme is guaranteed not to cause any extension or memory conflicts. It is the most simple way to protect your computer from kids, coworkers or anybody else for that matter while you are using your computer.