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, Windows X_X startup sound.

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

 * This is not really the last windows
 * This is only os with end of life with end of life with end of life x90