Launch date: September 14, 2000

Fatal flaw(s): Unreliable

They say you can't polish a turd, but damn did Microsoft try. We don't think we're going overboard when we say Windows ME was, without a hint of doubt, the worst operating system ever produced by Microsoft. It was prone to crashing and more unreliable than a Gucci Mane probationary period. It was a headache to install it, run it, install programs into it, clear it of viruses, and to even turn it off. It was remarkable how bad it was.