Windows only: Programmer and dad Scott Hanselman wanted an easy way to let his toddler play on his computer without deleting files or quitting programs, so he put together baby-proofing software, Baby Smash!. Start up Baby Smash! and let the little one go to town on your keyboard.
As babies smash on the keyboard, coloured shapes, letters and numbers appear on the screen. Baby Smash will lock out the Windows Key, as well as Ctrl-Esc and Alt-Tab so your baby can't get out of the application. Pressing ALT-F4 will exit the application and Shift-Ctrl-Alt-O brings up the options dialog.
Similar to previously mentioned BabySplat, Baby Smash! is a free download for Windows only, donations requested.