Win. True X X

Last ever Windows. Released in 1α.

Windows X_X

The startup sound is a very loud, high pitched screeching noise.

The shutdown sound is a brief, screaming, hissing, "Goodwill towards men, I don't think so," and extremely loud, sad, and scary cacophony.

When crashes, it only shows the error code in red letters on a blank background.

For example, it reads 0x000000F4, which means CRITICAL_PROCESS_DIED.

Source: Windows Xth of X Versions R2 by CromaticTM.

Trivia

 * A section from the 4th line of this page (if you are reading this page on the desktop), which reads "screaming, hissing, 'Goodwill towards men? I don't think so,'" is a reference to a line from 4:35 to 4:38 in Mystery Science Theater 3000 episode, "The Christmas That Almost Wasn't."
 * This is not really the last windows
 * This is only os with end of life with end of life with end of life x90