SosumiApple Computer's System 7 operating system. Popular rumor has it that the sound's unusual name was coined after a legal settlement with Apple Records, the Beatles' recording company. The sound itself is a sample of a xylophone strike.
Apple Records sued Apple Computer for trademark infringement after Apple Computer added sound to their computers. The lawsuit was settled with the agreement that Apple Computer would never enter the recording industry. Several years later, Apple Computer began adding microphones as standard peripherals with their computers. These microphones were for recording (of course), and as the story goes, the Apple developers named one of the sample sounds "Sosumi" ("So sue me") as a way of thumbing their noses at Apple Records. Apple Records did not sue.
The sound is still being used in modern versions of Mac OS, including Mac OS X.