Apple Computer, Inc. v. Microsoft Corp. - Wikipedia.
it’s a two way street lol both microsoft and apple have been sued (and also have sued) for copyright infringement in the past… either way, it’s a moot point IMO. At any rate, still an intresting read 
Apple claimed the “look and feel” of the Macintosh operating system, taken as a whole, was protected by copyright, and that each individual element of the interface (such as the existence of windows on the screen, the fact that they are rectangular, the fact that they are resizable, the fact that they overlap, and the fact that they have title bars) was not as important as all these elements taken together. After long argument, the judge insisted on an analysis of specific GUI elements that Apple claimed were infringements. Apple came up with a list of 189 GUI elements; the judge decided that 179 of these elements had been licensed to Microsoft in the Windows 1.0 agreement, and most of the remaining 10 elements were not copyrightable—either they were unoriginal to Apple, or they were the only possible way of expressing a particular idea.
In an odd twist midway through the suit, Xerox filed a lawsuit against Apple, claiming Apple had infringed copyrights Xerox held on its GUIs. Xerox had invested in Apple and had invited the Macintosh design team to view their GUI computers at the PARC research lab; these visits had been very influential on the development of the Macintosh GUI. Xerox’s lawsuit appeared to be a defensive move to ensure that if Apple v. Microsoft established that “look and feel” was copyrightable, then Xerox would be the primary beneficiary, rather than Apple. The Xerox case was dismissed because the three year statute of limitations had passed (i.e. Xerox waited too long to file suit.)
In recent years, Apple has resumed threats of litigation in this area. A common target has been Stardock, whose CEO Brad Wardell once joked that Apple’s lawyers had him on speed-dial. Apple was not pleased when skins and themes for WindowBlinds, IconPackager and DesktopX looking similar to their Aqua GUI were released in mid-2000, over six months before the release of Mac OS X.
Apple has also copied certain innovations from other companies: tabbed dialogs on Macintosh appeared after IBM used them in OS/2. Since the original settlement of the lawsuit, many features of the Macintosh and Windows GUIs have been incorporated into the windowing environments of unrelated third-parties, such as OpenWindows, X11, and Solaris. While it could be argued that the Mac OS X dock is stolen from the Windows taskbar, the Mac OS dock is actually derived from the NeXTSTEP dock (Mac OS X itself originating from NeXTSTEP). However, the idea of a program taskbar or dock is a major design feature of RISC OS, which already featured its so-called iconbar as early as 1987.