Apple's last OS to use the "Classic" interface. Described by PC World as "Apple's last flogging of the dead horse that is the classic Mac OS". It was extremely buggy and it liked to crash every time you were doing something important. (see POS) Even though it sucked it is still 100,000,000,000,000 times better than any version of Windows.
I just bought my iMac G3! It has Mac OS 9 on it.
Wow does it suck?
Yeah, but at least it's not Windows.