Apple Computer, Inc. v. Franklin Computer Corp.
The Franklin Ace 100.
The first Apple computer, appropriately named the Apple I, was a revolution in home computer design, but it was the Apple II that brought commercial success to Apple Computers. The Franklin Ace 100 was almost a complete clone of the Apple II.
Franklin copied large portions of Apple's operating system software in order to allow its computer run Apple programs*. In a time before hard disk drives, the operating system was stored on ROM chips.
Even though Franklin Computer lost this case, the company survived and is now one of the largest producers of non-smartphone hand-held electronic devices, including the now-defunct eBookman (an early e-reader). They currently make dictionaries, translators, and electronic Bibles. Apple has long refused to license the production of its hardware to third parties. As a result, it retains a monopoly on producing Apple-compatible computers.
*This link opens a FTP site containing disk images from hundreds of old Apple II-compatible programs.