Apple Macintoshes run their own operating system, also made by apple. They are collectively known as MacOS, although there are several major versions. Version 7 was around at the time of windows 3.1, but everyone chose the inferior system anyway... Versions 8.5 through to all versions of 9 is the more familiar look and feel, and the latest, Mac OS X (pronounced OS ten) is a complete re-write that has a FreeBSD and Mach based kernel.
I think version 8 coincided with Apple's move from Motorola 680x0 CPUs to PowerPC CPUs.
