Also, the coolest program in the xscreensaver package, period.

"The finest in personal computer emulation, this hack simulates popular screen savers from a number of less robust operating systems. Written by Jamie Zawinski."

This has, not only the Windows NT BSOD, but the Windows 9x BSOD, the Mac ROM's "Sad Mac" icon, some sort of Mac OS debugger, an Amiga error screen, and more.